The U.S. Postal Service affirmed Tuesday that it will not make a required $5.5 billion payment due Wednesday to the U.S. Treasury for future retirees' health care costs, Bloomberg News reported.

The Postal Service says the obligation must end in order for the public agency to become financially viable.

Reuters reported Monday that the mail agency, which relies on sales of stamps and other products rather than taxpayer funds, has said the same about a second payment due at the end of the fiscal year in September.

Missing the health pre-payment, the first default in the agency's history, would not cause interruptions in service or prevent the Postal Service from paying suppliers and employees, USPS spokesman David Partenheimer said in an e-mail, Reuters reported.