The idea to cut Saturday mail but keep six-day package delivery — a plan Postmaster General Patrick Donahoe estimated could save $2 billion — played up the agency's strong point.
Its package service is growing as more people buy things online, while the volume of letters sent has slumped with increased use of email and other internet services.
Over the past several years, the Postal Service also has advocated shifting to a five-day delivery schedule for mail and packages. It repeatedly but unsuccessfully appealed to Congress to approve the move and to free it from the advance health payments.
The Senate last year passed a bill that would have stopped the Postal Service from eliminating Saturday service for at least two years and required it to try two years of aggressive cost cutting instead. The House didn't pass a bill.
In dire straits, the agency acted on its own on the Saturday issue.
Issa said the reversal "significantly undercuts the credibility of postal officials who have told Congress that they were prepared defy political pressure and make difficult but necessary cuts."
Sen. Tom Carper, D-Del., a leader on postal issues, said he hoped Congress would pass new legislation to address the agency's problems.
President Barack Obama's budget proposal Wednesday includes the same provision as last year on the Post Service — a plan to let the agency realign its business plan to better compete in the changing marketplace.
The spending blueprint from the budget year that begins Oct. 1 includes a proposal for short-term financial relief and long-term changes at the agency that, it says, will result in more than $20 billion in savings over 10 years.