This post was updated at 11:34 a.m.

The financially struggling U.S. Postal Service announced Wednesday that it plans to stop delivering mail on Saturdays starting the week of Aug. 5 — but will continue delivering packages.

Unless forbidden to do so by Congress, which has moved in the past to prohibit five-day-a-week delivery, the agency for the first time will delivery mail only Monday through Friday. The move will save about $2 billion a year for the Postal Service, which has suffered tens of billions of dollars in losses in recent years with the advent of the Internet and e-commerce, officials said.

“The American public understands the financial challenges of the Postal Service and supports these steps as a responsible and reasonable approach to improving our financial situation,” Postmaster General Patrick R. Donahoe said at a news conference. “The Postal Service has a responsibility to take the steps necessary to return to long-term financial stability and ensure the continued affordability of the U.S. Mail.”

The postal service plans to continue Saturday delivery of packages, which remains a profitable and growing part of the delivery business. Post offices would remain open on Saturdays so that customers can drop off mail or packages, buy postage stamps or access their post office boxes, officials said. But hours likely would be reduced at thousands of smaller locations, they said.

At the White House, press secretary Jay Carney said President Obama does not have an opinion on the USPS announcement. He noted that the Postal Service is an independent agency and said the White House  learned of the news only on Tuesday.

“We put forward a year and a half ago a series of proposals for reform of the Postal Service that would put it on much more firm financial ground, and it passed the Senate,” Carney said. “Unfortunately, the House failed to take it up. So it would be our preference that that comprehensive package of reforms be implemented for the sake of a stronger future Postal Service.”

The Postal Service said it suffered a $15.9 billion net loss for fiscal 2012, which ended Sept. 30. That’s three times the loss recorded a year earlier.

The Postal Service has pushed to cancel Saturday mail delivery for years. It announced the decision Wednesday without congressional approval, even though lawmakers have argued that their consent is necessary to make the operational change. Postal officials are expected to argue that they do not need congressional action to halt Saturday delivery.

In the past, Congress has included a ban on five-day-a-week mail delivery in its appropriations bill. But the Postal Service is currently operating under a temporary spending measure, rather than an appropriations bill, and the agency is asking Congress not to reimpose the restriction when the spending measure expires March 27.

Sen. Thomas R. Carper (D-Del.), who has co-sponsored legislation in the past to reform postal services, said in a statement that he was “disappointed” that the Postal Service acted without congressional approval, but also understood that change was urgently needed.

“It’s hard to condemn the postmaster general for moving aggressively to do what he believes he can and must do to keep the lights on at the Postal Service,” said Carper, who recently became chairman of the Senate Homeland Security and Governmental Affairs Committee, which has federal workplace issues on its broad agenda.

Carper said he hopes to push through comprehensive reform legislation this congressional session. “Piecemeal efforts like the one the Postal Service announced today will not be enough to solve the Postal Service’s financial challenges for the long haul,” he said.

A majority of Americans support ending Saturday mail, according to national polls conducted in recent years, and President Obama has proposed halting deliveries as part of his budget-cutting proposals. Though the Postal Service is a quasi-governmental, self-funding entity, its worker compensation and retirement plans are tied to the federal budget.

Lawmakers have tried unsuccessfully for years to enact a significant overhaul of the Postal Service, hoping to reshape the agency as a leaner organization that delivers mail less frequently and operates fewer post offices across the country.

The Senate last year passed a bipartisan measure that would have permitted an end to Saturday mail delivery only after USPS conducted two years of feasibility studies. But postal officials — and some GOP lawmakers — opposed that plan, arguing that reams of professional studies and a declining balance sheet already proved that the change was needed.

A Republican-backed postal reform bill cleared a key committee last year but was never considered by the full House. The GOP bill would have permitted ending Saturday mail deliveries within a year.

Opposition to significant changes rests mostly with lawmakers from far-flung rural communities, who fear that a change in schedules could jeopardize low-cost delivery of medicines and medical supplies to elderly customers. The publishing industry also has complained that any changes would force quicker magazine publication deadlines and require some publishers to seek private delivery options instead, likely raising newsstand prices.

In a statement Wednesday, Jeannette P. Dwyer, president of the National Rural Letter Carriers’ Association, said the USPS announcement amounts to “yet another death knell for the quality service provided by the U.S. Postal Service.”

“For decades, the Postal Service has upheld a personal and professional standard of service, delivering to every household nationwide six days a week,” Dwyer said. “To erode this service will undermine the Postal Service’s core mission and is completely unacceptable.”

Joe Davidson and Josh Hicks contributed to this report.

Read more from Washington Post Politics: