The U.S. Postal Service is on the brink of default on a second multibillion-dollar payment it can't afford to pay.

Postmaster General Patrick Donahoe says the agency will be forced to miss the $5.6 billion payment due to the Treasury on Sunday, its second default in as many months.

For more than a year the Postal Service has been seeking legislation that would allow it to eliminate Saturday mail delivery and reduce its payment for future retiree health benefits. Congress has left Washington until after the November elections.

Donahoe says he's squeezed out all the cost savings within his power. The post office will hit a low point in cash next month but avert immediate bankruptcy due to employee reductions.

He says it's up to Congress to pass postal reform.