The U.S. Postal Service is pleading with Congress to step in and help as the agency inches closer to insolvency.

For the second time in as many months, USPS finds itself unable to pay the $5.6 billion federal law requires it to pay to fund health care benefits on retirees. The problems are only expected to get worse if Congress doesn't act: the agency could run out of cash before the end of October. Holiday mail might allow it to stay afloat a little longer, but by spring, it could run out of money for good.

Congress is refusing to address the Postal Service's financial woes until after the presidential election at the earliest--and more likely not until 2013.

The refusal to give USPS immediate attention has angered many USPS employees and unions, who blame Congress for the agency's financial problems in the first place.

"The payment in question results from an unnecessary congressional mandate--an obligation not required of any other company or agency in the country," National Association of Letter Carriers President Fredric Rolando told CNN.

Congress passed a law in 2006 requiring the prefunding of retiree benefits. The law was intended to help lower the federal deficit.

The Senate passed a bipartisan bill in April to help USPS, but House Republicans balked at the cost and drafted their own bill, which has still yet to go beyond a committee.

Republican Rep. Darrell Issa, who wrote the House bill, has however reached out to President Obama in recent weeks asking him to consider certain parts of the bill.

If the agency does run out of money, mail delivery is not expected to be impacted at this time; the Postal Service has a back-up plan for financial emergencies. But the agency may not be able to pay employees and sub-contractors.