* Some lawmakers say language allows USPS wiggle room
* Say service can change what it delivers Saturdays
* Postal Service lost $16 billion last year, needs help
Congress foiled the financially beleaguered U.S. Postal Service's plan to end Saturday delivery of first-class mail on Thursday when it passed legislation requiring six-day delivery.
The Postal Service, which lost $16 billion last year, had said last month it wanted to switch to five-day mail service to save $2 billion annually.
No law requires the Postal Service to deliver mail six days a week, but Congress traditionally has included a provision in legislation to fund the federal government each year that has prevented the Postal Service from reducing delivery service.
The Postal Service had asked Congress not to include the provision this time around.
Despite the request, the House of Representatives on Thursday gave final approval to the legislation that maintains the provision, sending it to President Barack Obama to sign into law. The Senate approved the measure on Wednesday.
But some lawmakers who support the Postal Service's plan have said there may still be some room for it to change its delivery schedule. They point out that the language requiring six-day delivery is vague and does not prohibit altering what products it delivers on Saturdays.
The Postal Service has said that while it would not pick up or deliver first-class mail, magazines and direct mail, it would continue to deliver packages and pharmaceutical drugs on Saturdays.
Republican Senator Tom Coburn of Oklahoma and Representative Darrell Issa of California on Thursday jointly told the USPS Board of Governors to move forward with implementing the five-day delivery plan for mail.
"The Board of Governors has a fiduciary responsibility to utilize its legal authority to implement modified 6-day mail delivery as recently proposed," the lawmakers said in their letter to the USPS board.
The Postal Service, they said, is in such dire financial need that it must implement all measures to fix its troubles.
LEGALITY IN QUESTION
Several polls have shown a majority of the public supports ending six-day delivery of first-class mail.
The plan for a new delivery schedule, Postal Service spokesman David Partenheimer said, would respond to the customers' changing needs and help keep the Postal Service from becoming a burden to taxpayers.
Last week, Coburn introduced an amendment to the spending bill to strike down the requirement for six-day mail delivery and give the mail carrier more control over its operations. That amendment failed.
A number of lawmakers and trade groups said the plan to cut Saturday mail service is illegal because the Postal Service requires Congress' approval before it makes such a decision.
Democratic Representative Gerald Connolly of Virginia said in a letter to the Government Accountability Office on Thursday that the Postal Service is still bound by the six-day requirement.
"Unfortunately, the Postmaster General continues to stonewall members of Congress, withholding his legal justifications for eliminating Saturday delivery from postal customers and the American public," Connolly said.
The Postal Service, an independent agency not funded by taxpayers, has said it could need a taxpayer bailout of more than $47 billion by 2017 if Congress does not give it flexibility to change its business model.
It had planned to drop Saturday first-class mail delivery in August.
Ending six-day first-class mail delivery is part of the Postal Service's larger plan to cut costs and raise revenues.
The mail carrier loses $25 million each day, as more Americans communicate by email and the Internet, and as heavy mandatory payments into its future retirees' health fund take a toll.
The Postal Service could run out of money by October if Congress does not provide legislative relief, some experts have estimated.
"Once the delivery schedule language ... becomes law, we will discuss it with our Board of Governors to determine our next steps," Partenheimer said.