WASHINGTON- The U.S. Postal Service said Thursday it placed an initial $2.98 billion order for 50,000 next-generation delivery vehicles from Oshkosh Corp and will double its initial planned EV purchases.

U.S. Postmaster Louis DeJoy said that based on USPS's ongoing reform efforts and "our improving outlook, we have determined that increasing our initial electric vehicle purchase from 5,000 to 10,019 makes good sense from an operational and financial perspective."

DeJoy previously committed to buying at least 10% EVs as part of its multibillion-dollar plan to retire its 30-year-old delivery vehicles.

USPS in February rejected a bid by the White House and Environmental Protection Agency to reconsider its plans to buy mostly gasoline-powered vehicles and hold a new hearing.

USPS said it expects the vehicles will begin appearing on carrier routes in late 2023.

In February last year, the USPS announced an initial $482 million contract for Oshkosh and said it could order up to 165,000 vehicles over 10 years in a deal that could be worth $6 billion or more.

The modern vehicles will replace many older USPS vehicles that lack air bags and other safety equipment as well as air conditioning.

Oshkosh said its "contract allows the flexibility, when funding is provided, to increase the percentage of (electric vehicles) to be produced even after an order is placed."

On Friday, a group of U.S. lawmakers asked Oshkosh if it sought to avoid using union workers by deciding to build the vehicles in South Carolina.

On Monday, lawmakers asked the Postal Service Office of Inspector General (OIG) to review USPS's vehicle purchase plan.

The inspector general's office said it "will be doing additional work in response to that request."

USPS said last week its commitment to "an electric fleet remains ambitious given the pressing vehicle and safety needs of our aging fleet as well as our fragile financial condition."

(Reporting by David Shepardson; editing by Jason Neely, Kirsten Donovan)