Attorneys general from 16 states and the District of Columbia launched a legal challenge against the United States Postal Service on Thursday, claiming that it violated the law when it ordered thousands of new mail trucks powered by gasoline instead.

Three lawsuits filed in two different federal courts raise the stakes of a conflict over the climate impacts of the Postal Service's delivery trucks that has roiled the administration for months.

Gerald Connolly, a leading House Democrat from Virginia, called for the resignation of the postmaster general after he disobeyed President Biden's order toelectrify the federal fleet.

The Postal Service is not bound by the administration's climate rules. One of the largest civilian fleets in the world has more than 231,000 vehicles. The contract would be the Postal Service's first large-scale vehicle purchase in three decades.

Environmentalists said that Mr. DeJoy's order of 165,000 gasoline-powered mail delivery trucks could hurt the nation's effort to combat climate change. The president promised to advance environmental policies that would grow union jobs, but the U.A.W. said that the new trucks would be built in nonunion factories.

The president relied on the support of environmental activists and union workers to win the White House in 2020.

The environmentalists, the union and the Democratic attorneys general of California, New York, Delaware, Pennsylvania, Michigan, Illinois and 10 other states all said that the move was illegal.

The Postal Service was found to have violated the 1970 National Environmental Policy Act by not considering the environmental impacts of the vehicle purchase.

The attorneys general wrote that the Postal Service chose a manufacturer with minimal experience in producing electric vehicles, signed a contract, and made a substantial down payment for new vehicles.

The Postal Service conducted a thorough review and fully complied with all of their obligations, according to Frum.

The decision to purchase gasoline-powered trucks, rather than more expensive electric trucks, took into account the financial troubles of the Postal Service, which is currently about $206.4 billion dollars in debt. A bipartisan law was signed by Mr. Biden earlier this month.

The Postal Service is committed to the inclusion of electric vehicles as a significant part of our delivery fleet even though the investment will cost more than an internal combustion engine vehicle. We must make fiscally prudent decisions in the introduction of a new vehicle fleet.

The new vehicles would get 29.9 miles per gallon according to the Postal Service. The E.P.A. found that the vehicles could only achieve 14.7% of that. The new trucks would only get 8.6 miles per gallon with the air-conditioning running.

While mail delivery trucks make up a tiny fraction of the roughly 280 million vehicles on the road in the U.S., environmental groups said the decision to order new gasoline-powered replacements could be consequential. An all-electric fleet would deliver environmental benefits and help an emerging manufacturing sector, but also serve as a powerful symbol of an administration that is determined to speed the transition away from fossil fuels.

Instead of moving forward with common-sense and available technology to mitigate the climate crisis, the USPS has decided to keep polluting communities at a time when federal agencies should be leading the way on electrification.