An electric service rates case before federal regulators could spell the end for a number of coal units operated by one of North Dakota’s largest electric cooperatives.

State regulators at the Public Service Commission are intervening in the case to try to thwart that possibility.

Bismarck-based Basin Electric Power Cooperative faces three challenges to its rates request before the Federal Energy Regulatory Commission. What caught the eyes of state regulators in November were filings by representatives from the Sierra Club, a nonprofit environmental advocacy organization, which argue that reimbursements for operations and upgrades at some of Basin’s coal-fired power plants should not be allowed in its rates.

In FERC filings, Basin has argued that not being allowed to collect reimbursements for the units could cause the co-op to default on some contracts — lowering its credit rating — and that closures, or changes to the operations, of the coal plants could hinder electric reliability in the area.

The state PSC does not regulate power cooperatives’ rates, but in its intervention in the case, commissioners share Basin’s view that closure of coal units in the region could harm reliability for the utilities they do regulate. The intervention was accepted by FERC in December. The commission has hired John Shepherd, an attorney with Washington, D.C.-based Hunton Andrews Kurth, to provide legal services for the case.