The United States Postal Service said Tuesday that it would add 66,000 electric vehicles to its fleet within the next five years, spending $9.6 billion to modernize its cars.

The "next generation delivery vehicles" will account for more than 75% of the 106,000 cars and trucks the USPS will purchase between now and 2028, a USPS press release said. After 2026, the USPS will exclusively purchase electric vehicles

The $9.6 billion price tag for the change will partially be covered by funds allocated through the Inflation Reduction Act (IRA), President Biden, and congressional Democrats' landmark climate, health care, and tax law.

Tuesday's announcement from the USPS came as a relief to many, as it represented a stark shift from the service's previous electric vehicle proposal earlier this year. That proposal would have seen only 40 percent electric vehicles out of a full order of 84,000 delivery vehicles.

That deal came after an even less climate-friendly one that would have only seen 10,019 EVs being added to the fleet.

Democrats in Congress, state officials, and environmental activists decried the decision. Sixteen states, plus the District of Columbia, sued to block the 10 percent electric plan, as did some of the country's leading environmental groups.

The Sierra Club was one of the advocacy groups pressuring the USPS to lean more into electric vehicles. Following Tuesday's announcement, groups such as this one are relieved to see officials listened to their concerns.

"Instead of receiving pollution with their daily mail packages, communities across the U.S. will get the relief of cleaner air," Katherine Garcia, director of the Sierra Club's Clean Transportation for All campaign, said in a statement on Tuesday.

The USPS maintains the single largest federal vehicle fleet, and a majority gas-powered fleet would have significantly hindered the Biden administration's target of net-zero-emissions federal government operations by 2050.

Now that the USPS is expanding with climate concerns in mind, it will have the potential to roll out one of the largest electric vehicle fleets in the country, said Postmaster General Louis DeJoy in a statement.

"We have a statutory requirement to deliver mail and packages to 163 million addresses six days per week and to cover our costs in doing so — that is our mission," DeJoy said. "As I have said in the past, if we can achieve those objectives in a more environmentally responsible way, we will do so."

Electric USPS vehicles are not likely to dominate the road for long, as shipping competitors Amazon and FedEx have also begun the shift away from gas-guzzling delivery vans. Amazon ordered 100,000 Rivian EVs to be on the road by 2030, and FedEx has already reserved 2,500 electric delivery vans from GM-backed BrightDrop.