(Bloomberg) -- Vistra Corp., one of the largest power generators in Texas, accused units of pipeline operator Energy Transfer LP of levying additional charges to deliver natural gas to profit from rising demand ahead of a looming winter storm.

Two Vistra units filed a complaint Tuesday to the Texas Railroad Commission, which oversees the oil and gas industry, requesting action against the pipeline firm over a plan to charge a premium when electricity prices at certain hubs exceeds $500 a megawatt-hour.

Energy Transfer didn’t immediately respond to an emailed request seeking comment sent outside office hours. Vistra declined to comment. 

The strategy to add a premium to some gas supply prices, known as the Ercot Price Adder, is “designed to capitalize on rising natural gas prices as Texans face the risk of freezing in the dark,” the Vistra units said in their complaint. The units asked the commission to order Energy Transfer to comply with an earlier pricing agreement and to launch enforcement action over alleged violations of price gouging rules. 

Plunging temperatures are poised to test the main Texas grid in coming days and expectations of record winter demand have already sent electricity prices for Friday surging. On-peak power for Ercot’s North hub closed at $800 for Feb. 4 on the Intercontinental Exchange, according to traders. 

Vistra and units of Energy Transfer had already been in a payment dispute over last year’s catastrophic Texas storm. The units last month threatened to cut service to Vistra over $21.6 million owed in fees from February 2021. Vistra has argued those fees are illegal.

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