Americans can still send and receive mail, but the U.S. Postal Service may not have much left in the bank after this week, as it's set to announce billions of dollars in losses as early as Thursday.

It's also waiting for postal regulators to announce Thursday whether they approve of a proposed 5.6 percent postage-rate increase, to start in January. The proposed increase faces stiff resistance from business groups and lawmakers, who say that the USPS should instead make deeper spending cuts to meet its financial obligations.

GOP opposition kept Congress from permitting the Postal Service to postpone paying $5.5 billion required by law to pre-fund retiree health benefits. A temporary spending measure to fund most federal programs through early December didn't mention the Postal Service; it passed the Senate on Wednesday and is expected to clear the House on Thursday.

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"The Postal Service does not want to make the tough decisions, which include cuts in personnel, pay and benefits. Instead, they are relying on a generous taxpayer bailout that will not solve any of their mid- or long-term problems," said Rep. Darrell Issa (R-Calif.), who opposes the rate increase and congressional relief.

"Taxpayers should not be made to bail out a business-as-usual Postal Service," Issa said.

"While it appears that the continuing resolution will not include USPS funding, service will not be compromised while the administration works with Congress and USPS to ensure that they have the tools and authorities necessary to remain viable well into the future," the Office of Management and Budget said in a statement. The administration and Postal Service have met this week to determine what portion, if not all, of the payment can be made by the close of the fiscal year Thursday, the OMB said.

The Postal Service has cut $10 billion in spending since 2008 and continues to trim its workforce through attrition.

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Postmaster General John E. Potter canceled a Wednesday meeting with reporters that was meant to address the financial concerns.

"Ideally, what you'd like to do in the Postal Service is have access to about $5 [billion] to $6 billion in cash, whether that's borrowing ability or cash on the books," Potter said in an April interview that predicted this week's turn of events. "That's basically two payrolls. That's not a lot of breathing room. Without relief in the form of lowering our payments into the retirement trust fund this year, we are perilously close to running out of cash in October."

Strong mail volume this month might add enough revenue to justify making the $5.5 billion payment to the government, but it would still leave little in postal coffers, said sources familiar with the process but not authorized to speak on the record.

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Senate Democrats hope to introduce a bill during the lame-duck session that would give the Postal Service more flexibility to determine its delivery schedule and decide whether it needs to close thousands of branches. The bill, introduced by Sen. Thomas R. Carper (D-Del.), also addresses how USPS could make the $5.5 billion annual payments in the future.

"I think this entire situation puts more pressure on the Postal Service and pressure on the legislators to address the issue comprehensively," said Tony Conway, executive director of the Alliance of Nonprofit Mailers, which represents some of the mail agency's biggest and most loyal customers.