WASHINGTON — The U.S. Postal Service announced plans to add a day or more to its standards for first-class mail delivery, hike rates and reduce post office hours as it struggles with financial deficits.

“It is our path to financial sustainability and service excellence,” Postmaster General Louis DeJoy said on a teleconference Tuesday to announce what the service is calling a 10-year plan.

Current standards call for delivering first-class mail in one to three days. Under revised standards, delivery time would stretch to as much as five days, according to the Postal Service plan. It also said it would “align hours of operation” at low-traffic post offices.

The service said it will seek approval from the Postal Regulatory Commission to change the first-class service standards.

The modifications entail shifting mail “from unreliable air transportation to more reliable ground transportation,” the Postal Service said in a news release.

First-class mail traveling within a local area will continue to be delivered in one or two days, and 70% of first-class mail will still arrive in three days or less, the service said.

The plan calls for an additional $44 billion in revenue from “pricing flexibility” for mail categories including first-class mail.

DeJoy said he couldn’t predict how much a first-class stamp will go up. The service will use its rate authority judiciously, DeJoy said during a question-and-answer session with reporters.

“We are committed to delivering affordable service to the American people,” DeJoy said.

Mark Dimondstein, president of the American Postal Workers Union, which represents more than 200,000 workers, expressed “deep concerns” about parts of the plan. In an emailed statement he cited proposals to slow the mail, reduce access to post offices and “further pursue the failed strategy of plant consolidation.”

Dimondstein cited “positive attributes” such as plans to hire 11,000 workers at sorting facilities, and to invest $4 billion for initiatives including improving lobbies of local post offices and adding shipping consultants for small businesses.

Mail delivery has remained sluggish since slowing down last year after DeJoy cut overtime and extra trips by delivery trucks in an effort to rein in costs. DeJoy, a donor to former President Donald Trump, was appointed by a Republican-majority board last year.

Parts of the plan “will harm service for folks across the country,” said Sen. Gary Peters, the Michigan Democrat who is chairman of the Homeland Security and Governmental Affairs Committee that oversees the Postal Service.

“Cuts to service standards for first-class mail, limiting hours at local post offices, and making it more difficult for people to access postal products would adversely impact USPS customers across the nation,” Peters said.

Some Democratic members of Congress have called for replacing DeJoy. President Joe Biden can’t directly fire DeJoy, whose employment is decided by the independent agency’s board. Biden has nominated three new board members who would break Republican control of the body.