Brazos Electric Power Cooperative Inc., Texas’ largest and oldest electric power cooperative, filed for bankruptcy protection in federal court in Houston yesterday, citing a disputed $1.8 billion bill from the state’s grid operator Electric Reliability Council of Texas (ERCOT), according to Reuters. Brazos, which supplies electricity to more than 660,000 Texas consumers, is one of many providers facing astronomical charges associated with last month’s deep freeze.

Sub-freezing temperatures knocked out nearly half of the state’s power plants two weeks ago, leaving nearly 4.5 million people without heat for many days, along with bursting water pipes that caused residential and commercial damage.

The fallout threatens utilities and power marketers, both of which face billions of dollars in related charges. Brazos and other providers were required to buy replacement power at high rates and cover other firms’ unpaid fees.

Last week, ERCOT said $2.1 billion in initial bills went unpaid. More unpaid bills are expected. Citing the crisis situation, many are calling for ERCOT to suspend the service charges to halt additional defaults.

Denton went a step further and sued ERCOT to prevent the grid operator from charging the city for fees unpaid by other grid users. Denton Electric could face tens of millions of dollars for fees that were not collected from others, the suit claims.