The cutback would begin the week of Aug. 5. The move, which has been in talks for years, would save the Postal Service about $2 billion annually.
The agency has been operating in the red, forcing it to close post offices and distribution centers across the country.
The problem for the post office is technology. The delivery of letters and other mail has dramatically declined with the increasing use of email and other Internet use. But not all of the business is bad.
"Our package volume continues to grow through e-commerce," said Richard Maher, spokesman for the U.S. Postal Service. "Our package volume has grown 14 percent just in the last two years."
Package delivery will continue on Saturdays and post offices will remain open. Still reducing residential delivery on the weekends will cost jobs.
"We anticipate that this will reduce the number of our employees between 22,000-35,000, most of that we hope to accomplish through attrition," said Maher.
Over the past several years, the Postal Service has advocated shifting to a five-day delivery schedule for mail and packages - and it repeatedly but unsuccessfully appealed to Congress to approve the move. Though an independent agency, the service gets no tax dollars for its day-to-day operations but is subject to congressional control.
Congress has included a ban on five-day delivery in its appropriations bill. But because the federal government is now operating under a temporary spending measure, rather than an appropriations bill, Postmaster General and CEO Patrick R. Donahoe says it's the agency's interpretation that it can make the change itself.
In November, the USPS reported an annual loss of a record $15.9 billion for the last budget year and forecast more red ink in 2013, capping a tumultuous year in which it was forced to default on billions in retiree health benefit prepayments to avert bankruptcy.
The financial losses for the fiscal year ending Sept. 30 were more than triple the $5.1 billion loss in the previous year. Having reached its borrowing limit, the mail agency is operating with little cash on hand.
The Associated Press contributed to this report.