California's plan to ban sales of new gasoline cars in 2035 is already facing resistance from the federal government.

Environmental Protection Agency (EPA) boss Andrew Wheeler on Monday questioned the California plan in a letter, Reuters reported.

The plan "raises serious questions regarding its legality and practicality," Wheeler reportedly wrote.

Wheeler said an influx of electric cars could overwhelm California's power grid, citing recent rolling blackouts in the state. The state's grid operator blamed outages on a gas plant suddenly dropping offline, combined with lack of wind power and unavailability of imported power from other states. Diesel generators were used as a grid buffer.

He also said the ban on internal-combustion cars would require federal approval, and that it may require California to request a waiver from the EPA.

The EPA has already tried to revoke California's Clean Air Act waiver, which allows the state to set its own, stricter, emissions standards and mandate the sale of zero-emission vehicles.

Under the Trump Administration, the EPA has shifted focus from environmental protection to environmental deregulation, serving the interests of the very industries it is charged with monitoring.

Wheeler is a former coal lobbyist, and has been criticized for being too close to oil-company interests.

Under Wheeler, the EPA has dissolved independent boards of scientists that advised the agency on air pollution.

But California emissions rules fall into the realm of state's rights—something Republicans like President Donald Trump, and the judges they tend to appoint, normally champion.

That also means, even if Trump wins another term in next month's election, any EPA ruling against California's gasoline-car sales ban would face an uncertain future in the courts.