Postmaster General Patrick Donahoe is among the witnesses scheduled to appear Tuesday before the Senate Homeland Security and Governmental Affairs Committee.
The Postal Service is facing a second straight year of losses of $8 billion or more. A decline in mail because of the Internet and the loss of revenue from advertising amid the economic downturn have taken a toll on the agency.
Postal officials say they will be unable to make this month's $5.5 billion payment to cover future employee health care costs because the agency will have reached its borrowing limit and doesn't have enough cash.
The Postal Service has proposed ending Saturday mail delivery and is considering cutting as many as 120,000 jobs.