Congress is set to hold a hearing on the state of the U.S. Postal Service

— Congress is set to hold a hearing Tuesday on the state of the financially troubled U.S. Postal Service amid warnings of a possible default and new questions about the viability of America's current mail delivery system.

Possible money saving reforms to the service include a drop in mail delivery from six to five days a week.

Postmaster General Patrick Donahoe is set to testify before the Senate Homeland Security and Governmental Affairs committee at 2 p.m.

Officials have promised there will be no disruptions to mail delivery, employee payroll, or payments to suppliers if a default occurs. But as the total volume of mail delivered by the postal service continues to drop, administrators are warning of severe financial strains.

Among other things, the service lacks sufficient funds to make a required $5.5 billion payment to its retiree health care trust fund at the end of the month, according to spokeswoman Yvonne Yoerger.

The trust fund was mandated by a 2006 reform bill that postal officials contend no longer matches a reality of declining revenues and a smaller workforce.

Yoerger said Donahoe will argue at Tuesday's hearing that obligations to the fund should be changed in part to reflect a drop in the service's workforce from roughly 900,000 to 650,000 positions

In addition to relief from the future retiree payment mandate, Yoerger said a proposed business plan for the Postal Service would include a combination of closing post offices, expanding joint ventures with private industry, and changing the frequency of mail delivery.

"Right now we are required to deliver six days a week," she said. "If it can go to five days a week, as proposed, we could better match the declining volume of mail."