<?xml version="1.0" encoding="utf-8"?>
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <!-- INTEGIX by Ez-XBRL -->
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedLabel" roleURI="http://www.xbrl.org/2009/role/negatedLabel"/>
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedPeriodEndLabel" roleURI="http://www.xbrl.org/2009/role/negatedPeriodEndLabel"/>
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedPeriodStartLabel" roleURI="http://www.xbrl.org/2009/role/negatedPeriodStartLabel"/>
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedTotalLabel" roleURI="http://www.xbrl.org/2009/role/negatedTotalLabel"/>
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedNetLabel" roleURI="http://www.xbrl.org/2009/role/negatedNetLabel"/>
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/negated-2009-12-16.xsd#negatedTerseLabel" roleURI="http://www.xbrl.org/2009/role/negatedTerseLabel"/>
  <roleRef xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/role/net-2009-12-16.xsd#netLabel" roleURI="http://www.xbrl.org/2009/role/netLabel"/>
  <labelLink xlink:type="extended" xlink:role="http://www.xbrl.org/2003/role/link">
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_CommonSharesMember" xlink:label="loc_ck0001171471_CommonSharesMember_1"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_FacilityMember" xlink:label="loc_ck0001171471_FacilityMember_2"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_LoanMember" xlink:label="loc_ck0001171471_LoanMember_3"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesMember_4"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_5"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_6"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_7"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_8"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_9"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_10"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_11"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_12"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_13"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_14"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_15"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember" xlink:label="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_16"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_Notes2035Member" xlink:label="loc_ck0001171471_Notes2035Member_17"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_PreferredSharesMember" xlink:label="loc_ck0001171471_PreferredSharesMember_18"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_PreferredSharesMember" xlink:label="loc_ck0001171471_PreferredSharesMember_19"/>
    <loc xlink:type="locator" xlink:href="ck0001171471-20260904.xsd#ck0001171471_SeriesATermPreferredStockDue2025Member" xlink:label="loc_ck0001171471_SeriesATermPreferredStockDue2025Member_20"/>
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_21"/>
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_22"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_CommonSharesMember_0" xml:lang="en-US">Common Shares [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_FacilityMember_0" xml:lang="en-US">Facility [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_LoanMember_0" xml:lang="en-US">Loan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series C [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_1" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series C [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series D [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_1" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series D [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series E [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_1" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series E [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series G [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_1" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series G [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series H [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_1" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series H [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_0" xml:lang="en-US">Mandatory Redeemable Preferred Shares Series I [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_1" xml:lang="en-US">Mandatory Redeemable Preferred Shares.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_Notes2035Member_0" xml:lang="en-US">Notes 2035 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_PreferredSharesMember_0" xml:lang="en-US">Preferred Shares [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="lab_ck0001171471_PreferredSharesMember_1" xml:lang="en-US">Preferred Shares [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_ck0001171471_SeriesATermPreferredStockDue2025Member_0" xml:lang="en-US">Series A Term Preferred Stock Due 2025 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_us-gaap_ClassOfStockDomain_0" xml:lang="en-US">All Securities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_us-gaap_DebtInstrumentNameDomain_0" xml:lang="en-US">Debt Instrument Name [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_CommonSharesMember_1" xlink:to="lab_ck0001171471_CommonSharesMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_FacilityMember_2" xlink:to="lab_ck0001171471_FacilityMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_LoanMember_3" xlink:to="lab_ck0001171471_LoanMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesMember_4" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_5" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_6" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesCMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_7" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_8" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesDMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_9" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_10" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesEMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_11" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_12" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesGMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_13" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_14" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesHMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_15" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_16" xlink:to="lab_ck0001171471_MandatoryRedeemablePreferredSharesSeriesIMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_Notes2035Member_17" xlink:to="lab_ck0001171471_Notes2035Member_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_PreferredSharesMember_18" xlink:to="lab_ck0001171471_PreferredSharesMember_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_PreferredSharesMember_19" xlink:to="lab_ck0001171471_PreferredSharesMember_1"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ck0001171471_SeriesATermPreferredStockDue2025Member_20" xlink:to="lab_ck0001171471_SeriesATermPreferredStockDue2025Member_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ClassOfStockDomain_21" xlink:to="lab_us-gaap_ClassOfStockDomain_0"/>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_22" xlink:to="lab_us-gaap_DebtInstrumentNameDomain_0"/>
  </labelLink>
</linkbase>
