The postal service, which as independent agency of government relies on its own revenue from the sale of stamps and other products rather than taxpayer funds, has lost billions of dollars each quarter as Americans move online to pay bills and communicate.
It hit the limit in September, according to USPS spokesman David Partenheimer.
"We need passage of comprehensive legislation as part of our business plan to return to long-term financial stability," the spokesman said.
Congress left Washington without acting on legislation that might help the agency attain some financial stability. Nearly all legislation is on hold until after the U.S. presidential elections on Nov. 6.
The agency still had enough cash to make a $1.4 billion payment for workers compensation claims due on Monday, Partenheimer added.