A leading power grid regulator is sounding the alarm on President Joe Biden’s tough new rules for power plants. Mark Christie, who helps oversee the nation’s electric grid, says these rules could spell big trouble for keeping the lights on across America.

Christie, who works at the Federal Energy Regulatory Commission, shared his worries in a letter to Republican lawmakers this week. He didn’t mince words, calling the potential effects of these rules “catastrophic” if they go into effect.

The Environmental Protection Agency rolled out these new rules in April. They’re pushing coal plants to cut their emissions by a whopping 90% by 2032, or risk being shut down by 2039. Some new natural gas plants will also need to slash their emissions.

“This could force almost all remaining coal plants to close,” Christie warned. “It will also make it really hard to build new gas plants that we desperately need.”

Christie pointed out a big problem with the EPA’s plan. The technology they’re demanding — called carbon capture and storage — isn’t ready for prime time. “No power plants using this tech have been successful in today’s energy markets,” he explained.

The grid expert also highlighted a growing concern: as the U.S. shuts down reliable power plants, we’re not building new ones fast enough to keep up. This could lead to blackouts and brownouts in the future.

“Once these vital power plants close, they’re gone for good,” Christie cautioned. “We can’t just turn them back on if we need them later.”

As the debate over these rules heats up, it’s clear that keeping America’s lights on is becoming a hot-button issue in Washington.