WASHINGTON (AP) — With no financial relief in sight, the U.S. Postal Service is pushing ahead with planned cuts to more than 260 mail processing centers around the nation, part of a billion-dollar cost-cutting effort that will slow delivery of first-class mail.

In a statement Thursday, the cash-strapped agency said it had completed a review of closings to mail processing centers it had proposed last fall. Based on community input and other factors, the post office said, it will move forward with consolidations involving virtually all of the 252 facilities on the list, as well as up to 12 new locations, beginning in mid-May.

Of the 264 facilities, roughly 41 won't be closed or consolidated right away as the post office conducts additional reviews.

The consolidations are expected to result in a loss of roughly 35,000 jobs, which the post office hopes to achieve mainly through attrition. The agency described the move as a necessary cost-saving measure because of declining mail volume as people and businesses continue switching to the Internet in place of letters and paper bills.

The 12 locations added to the list include those in Owensboro, Ky.; Washington, Pa.; Cardiss Collins (Chicago), Ill.; Gaylord, Mich.; Staten Island, New York; Mankato, Minn.; Champaign, Ill.; Atlanta, Ga.; Corpus Christi, Texas; Fort Worth, Texas; Mid-Florida, Fla.; and Butte, Mont.

"The steps we are taking now will put the Postal Service on a strong financial footing for decades to come," the agency said in a statement.

The estimated $3 billion in reductions are part of a wide-ranging effort by the Postal Service to quickly trim costs, seeing no immediate help from Congress. It is seeking to close or consolidate more than half of its nearly 500 mail processing centers.

Because the consolidations typically would lengthen the distance mail travels from post office to processing center, the agency also would lower delivery standards for first-class mail that, for the first time in 40 years, will eliminate the chance for stamped letters to arrive the next day.

Last week, the Postal Service warned it will lose as much as $18.2 billion a year by 2015 unless Congress grants it new leeway to eliminate Saturday delivery and raise the price of a postage stamp by as much as 5 cents.

It is asking Congress for permission to make service cuts and reduce annual payments of about $5.5 billion to prefund retiree health benefits. At the request of Congress, the cash-strapped agency agreed to wait until mid-May to begin closures so lawmakers would have time to stabilize its finances first.

But in recent weeks, the Senate and House have stalled as lawmakers differ widely on costs, the level of financial oversight and the prospect of widespread postal closures.

The Postal Service, an independent agency of government, is subject to congressional control on major aspects of its operations. Earlier this month, the Postal Service said its quarterly loss ballooned to $3.3 billion amid declining mail volume and said it could run out of money by October.

Sen. Bernie Sanders, I-Vt., who is pushing for legislative changes that would stop or delay mass closings of mail processing centers, described the proposed closings as counterproductive. He and 26 other senators recently signed a letter to congressional sponsors of postal legislation seeking to prevent cuts to first-class mail delivery.

"At a time when the Postal Service is competing against the instantaneous delivery of information from email and the Internet, slowing down mail delivery service will result in less business and less revenue, and will bring about a death spiral for this institution," Sanders said.