WASHINGTON >> Democrats on the House Oversight Committee are seeking an investigation into a U.S. Postal Service plan to replace its aging mail trucks with mostly gasoline-powered vehicles.

The plan largely ignores White House calls to replenish the mail-service fleet with electric vehicles and has drawn sharp criticism from the Biden administration, Democratic lawmakers and environmentalists, who say it falls far short of President Joe Biden’s goals to address climate change.

In a letter Monday, Democrats on the oversight panel asked the agency’s inspector general to investigate whether the Postal Service complied with the National Environmental Policy Act and other laws when awarding a 10-year contract to Wisconsin-based Oshkosh Defense to supply up to 165,000 new mail trucks.

Only 10% of the initial order will be for EVs; the remaining 90% will use traditional gasoline-powered engines.

The Environmental Protection Agency, the White House Council on Environmental Quality and “numerous environmental stakeholders” have raised concerns that the Postal Service did not meet its NEPA obligations in issuing the contract, the lawmakers said in a letter to Tammy Whitcomb, the Postal Service inspector general.

“Given the substantial public interest in this acquisition and the significant deficiencies” in the environmental analysis identified by EPA and the White House, “it is critical that Congress understand whether the Postal Service properly met its statutory environmental obligations,” the lawmakers wrote.

The letter is signed by five Democratic lawmakers, including Rep. Carolyn Maloney of New York, the panel’s chair, and Gerry Connolly of Virginia, chairman of a subcommittee on government operations.

The lawmakers said they strongly support the purchase of electric vehicles for the Postal Service fleet, saying it would “significantly cut emissions and position the Postal Service as an environmental leader” in the U.S.

A spokeswoman said the inspector general’s office received the letter Monday and was reviewing it.

The Postal Service awarded Oshkosh Defense a contract worth up to $11 billion over 10 years to replace its 230,00-vehicle fleet. The company has said it will make the Next Generation Delivery Vehicles at a reconfigured warehouse in South Carolina, creating 1,000 new jobs.

The Postal Service said last month that it believes it has met all its obligations and is moving forward despite widespread criticism.

The agency “carefully reviewed and incorporated feedback” from EPA and the White House regarding the new contract and believes “there is no legal or other basis to delay the (vehicle-replacement) program,″ said spokeswoman Kim Frum.

The new contract will deliver 5,000 electric vehicles beginning in 2023 and “provides significant environmental benefits through the introduction of safer and more environmentally friendly vehicles,” Frum said. Flexibility built into the contract allows for more electric vehicles “should additional funding become available,” she added.

In their letter, lawmakers cited a host of concerns raised by EPA, including allegations that the contract was awarded before the environmental review was completed, and that the Postal Service omitted important data on climate change and other issues in completing the review.

The USPS review “underestimates greenhouse gas emissions” of the new fleet, “fails to consider more environmentally protective feasible alternatives and inadequately considers impacts on communities with environmental justice concerns,” the EPA said in a Feb. 2 letter.

The EPA called the proposal “a crucial lost opportunity to more rapidly reduce the carbon footprint of one of the largest government fleets in the world.” The mail-service fleet comprises more than 230,000 vehicles, nearly one-third of the federal government’s overall fleet.

The new vehicles are greener than current models, which have been in use for three decades or more, but most will be powered by gasoline.

An electrified fleet would save about 135 million gallons of fuel per year, said Adrian Martinez, an attorney for the environmental group Earthjustice who has urged the Biden administration to force the Postal Service to suspend or delay the contract and develop a more eco-friendly plan.

Postmaster General Louis DeJoy, a Republican donor and ally of former President Donald Trump, has said the 10% EV production is the best the Postal Service can do, given its “dire financial condition.” An additional $3.3 billion would be needed convert the entire USPS fleet to battery-powered electrics, DeJoy said.

The Postal Service decision conflicts with Biden’s goal to convert all of the federal government’s vehicles to zero-emissions models by 2035. The Postal Service is controlled by a board of governors and does not take orders from the president. Biden has nominated two people to serve on the board, but they have not been confirmed, leaving the panel under control of a Republican chairman, Roman Martinez.