The Environmental Protection Agency sent a letter to the Postal Service on Wednesday urging it to hold a new hearing on its 10-year contract with Oshkosh Corp that could be worth $6 billion or more to build up to 165,000 next-generation delivery vehicles.

White House Council on Environmental Quality chair Brenda Mallory said in a letter that EPA "has communicated grave concerns with the adequacy of the environmental review that the USPS has conducted to date." She urged USPS to complete a supplemental environmental impact statement.

USPS did not immediately comment.

USPS awarded a $482 million contract to Oshkosh's defense unit, which makes the vehicles, in February 2021 that could ultimately be worth $6 billion.

U.S. Postmaster General Louis DeJoy previously told lawmakers the agency was committed to having electric vehicles make up 10% of its next-generation fleet as part of its multibillion-dollar plan to retire its 30-year-old delivery vehicles.

Biden's spending and climate bill would award $6 billion for USPS to purchase electric delivery vehicles and infrastructure. USPS has said with the funding that "all delivery fleet acquisitions could feasibly be electric by 2028, and a corresponding 70% of our entire delivery fleet by" 2030 could be EVs.

Mallory wrote Wednesday that the White House supports USPS "using its existing resources, including its significant cash reserve or through a credit strategy, to invest in our nation's health, environment and competitiveness."

The contract allows for delivery of between 50,000 and 165,000 of the vehicles over 10 years.

The USPS rejected a proposal from electric-vehicle maker Workhorse Group.

DeJoy said last year USPS had agreed to spend $500 million on the next-generation vehicles to make them convertible to EVs from internal-combustion models at a future date.

(Reporting by David Shepardson and Chris Gallagher; Editing by Tim Ahmann and Aurora Ellis)

By David Shepardson