The US postal service (USPS) is facing the mounting fury of the Biden administration, Democratic lawmakers and environmental groups over its plan to spend billions of dollars on a new fleet of gasoline-powered mail delivery trucks that critics say will upend a White House goal to slash planet-heating gases.

The USPS has outlined plans to spend $11.3bn on as many as 165,000 new delivery trucks over the next decade to refresh what is one of the largest civilian vehicle fleets in the world. The familiar boxy white trucks with red and blue stripes will be replaced by a new design that has been likened in appearance to a duck.

A full 90% of the fleet, however, will have traditional gas-powered engines, with just 10% being electric. While the new trucks will come with air conditioning, this means their fuel efficiency will be strikingly poor at just 8.2 miles per gallon (3.56 km per litre).

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This is worse than all of the most popular gas-hungry trucks currently on sale in the US and is even less efficient than the original Hummer, a vehicle infamous for the vast amount of fuel it burned through. “We were optimistic the postal service would listen to us about the benefits of an electric fleet, but it doubled down on its inexplicable preference for polluting trucks,” said Adrian Martinez, senior attorney at Earthjustice.

The postal service’s truck contract with Oshkosh Corporation, a Wisconsin-based defence contractor, has sparked uproar within a Biden administration that has set a goal for the federal government to get to net zero emissions by 2050 in order to tackle the climate crisis. Transportation is the largest source of greenhouse gas emissions in the US and analysts have warned the transition away from gas and diesel cars must speed up if disastrous climate change is to be avoided.

The Environmental Protection Agency (EPA) has written to the USPS to complain that the new truck contract is “seriously deficient” in its appreciation of climate concerns. “The postal service’s proposal as currently crafted represents a crucial lost opportunity to more rapidly reduce the carbon footprint of one of the largest government fleets in the world,” wrote Vicki Arroyo, the EPA’s associate administrator for policy.

Some commercial delivery operators have started to look closely at electric trucks to meet corporate climate goals and realize the cost savings of running vehicles that generally require less maintenance, and run on cheaper fuel, than the traditional gas option. Amazon, for example, has ordered 100,000 electric trucks from the electric vehicle company Rivian.

The USPS, however, has said that it is in a “perilous” financial situation and that it has to choose the most reasonable contract to meet its obligations of delivering to 161m different addresses across the US.

“Our commitment to an electric fleet remains ambitious given the pressing vehicle and safety needs of our aging fleet as well as our dire financial condition,” said Louis DeJoy, the USPS postmaster general.

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“When you’re an independent government entity running billion-dollar annual losses, and with a congressional mandate to operate in a financially sustainable manner, we are compelled to act prudently in the interests of the American public.”

The controversy has heightened Democratic calls for the removal of DeJoy, a major donor to Donald Trump who has remained in his post following the previous president’s election loss. The USPS board of governors, which Biden controls appointments to, holds the power to fire postmaster generals.

“The postal service urgently needs a change in leadership,” said Sheldon Whitehouse, a Democratic senator from Rhode Island. “Under postmaster general DeJoy, the postal service is actively choosing to ignore science and the law in order to make sure one of the world’s largest fleets of government vehicles continues to be a major source of pollution.

“Postmaster General DeJoy has messed around with our mail system for too long and he’s caused real harm to the Americans who rely on it. This cannot continue.”