LEGAL	9 Months Ended
Sep. 30, 2026
Commitments and Contingencies Disclosure [Abstract]
LEGAL	LEGAL Other than as disclosed below or in Tri-State's annual report on Form 10-K for the year ended December 31, 2025 filed with the SEC, Tri-State does not expect any litigation or proceeding pending or threatened against it to have a potential material effect on its financial condition, results of operations or cash flows. NRPPD Section 206 Complaint: On March 25, 2024, Northwest Rural Public Power District ("NRPPD") filed a Federal Power Act ("FPA") section 206 proceeding with FERC, Docket No. EL24-93, against Tri-State and Basin Electric Power Cooperative ("Basin") asking FERC to exercise primary jurisdiction over the interpretation of FERC's December 19, 2023 order related to Tri-State's contract termination payment tariff and Tri-State's Amended and Restated Wholesale Power Contract for the Eastern Interconnection with Basin ("Basin Eastern WPC"). In particular, NRPPD requested that FERC hold that NRPPD’s withdrawal from Tri-State is permissible under the Basin Eastern WPC and that NRPPD’s contract termination payment calculation is the appropriate contract termination payment. On December 5, 2024, FERC issued an order denying NRPPD's complaint because NRPPD failed to satisfy its burden under FPA section 206. FERC's order also determined that NRPPD's withdrawal from Tri-State does not cause a breach of the Basin Eastern WPC ("FERC NRPPD Order"). On February 13, 2025, Basin filed a petition for review of the FERC NRPPD Order, Case No. 25-1060, with the United States Court of Appeals for the District of Columbia Circuit ("DC Circuit Court of Appeals"). On March 17, 2025, Tri-State filed a notice of intervention in Basin's petition for review. On October 2, 2026, the DC Circuit Court of Appeals issued an opinion denying Basin's petitions for review and affirming FERC's determination that NRPPD's withdrawal from Tri-State does not cause a breach of the Basin Eastern WPC. Las Tusas Fire. In the first quarter of 2026, Tri-State was added as a co-defendant to an existing lawsuit against its Utility Member, Mora San Miguel Electric Cooperative, Inc. (“MSMEC”), relating to the Las Tusas fire that occurred in May 2023 in San Miguel County, New Mexico. Tri-State’s operations, assets or personnel are not alleged to be the cause of the fire. Rather, it is alleged that MSMEC’s facilities started the fire and that Tri-State had influence over or oversight of MSMEC’s activities. Tri-State filed an answer to the amended complaint on May 20, 2026. Tri-State plans a vigorous defense in close coordination with its insurance carrier and with primary defense costs covered by insurance. It is not possible to predict the outcome of this matter or whether Tri-State will incur any resulting liability.

Other than as disclosed below or in Tri-State's annual report on Form 10-K for the year ended December 31, 2025 filed with the SEC, Tri-State does not expect any litigation or proceeding pending or threatened against it to have a potential material effect on its financial condition, results of operations or cash flows.

NRPPD Section 206 Complaint: On March 25, 2024, Northwest Rural Public Power District ("NRPPD") filed a Federal Power Act ("FPA") section 206 proceeding with FERC, Docket No. EL24-93, against Tri-State and Basin Electric Power Cooperative ("Basin") asking FERC to exercise primary jurisdiction over the interpretation of FERC's December 19, 2023 order related to Tri-State's contract termination payment tariff and Tri-State's Amended and Restated Wholesale Power Contract for the Eastern Interconnection with Basin ("Basin Eastern WPC"). In particular, NRPPD requested that FERC hold that NRPPD’s withdrawal from Tri-State is permissible under the Basin Eastern WPC and that NRPPD’s contract termination payment calculation is the appropriate contract termination payment. On December 5, 2024, FERC issued an order denying NRPPD's complaint because NRPPD failed to satisfy its burden under FPA section 206. FERC's order also determined that NRPPD's withdrawal from Tri-State does not cause a breach of the Basin Eastern WPC ("FERC NRPPD Order"). On February 13, 2025, Basin filed a petition for review of the FERC NRPPD Order, Case No. 25-1060, with the United States Court of Appeals for the District of Columbia Circuit ("DC Circuit Court of Appeals"). On March 17, 2025, Tri-State filed a notice of intervention in Basin's petition for review. On October 2, 2026, the DC Circuit Court of Appeals issued an opinion denying Basin's petitions for review and affirming FERC's determination that NRPPD's withdrawal from Tri-State does not cause a breach of the Basin Eastern WPC.

Las Tusas Fire. In the first quarter of 2026, Tri-State was added as a co-defendant to an existing lawsuit against its Utility Member, Mora San Miguel Electric Cooperative, Inc. (“MSMEC”), relating to the Las Tusas fire that occurred in May 2023 in San Miguel County, New Mexico. Tri-State’s operations, assets or personnel are not alleged to be the cause of the fire.

Rather, it is alleged that MSMEC’s facilities started the fire and that Tri-State had influence over or oversight of MSMEC’s activities. Tri-State filed an answer to the amended complaint on May 20, 2026. Tri-State plans a vigorous defense in close coordination with its insurance carrier and with primary defense costs covered by insurance. It is not possible to predict the outcome of this matter or whether Tri-State will incur any resulting liability.