But change is not the biggest factor in the agency's predicament â¿¿ Congress is. The majority of the service's red ink comes from a 2006 law forcing it to pay about $5.5 billion a year into future retiree health benefits, something no other agency does. Without that payment â¿¿ $11.1 billion in a two-year installment last year â¿¿ and related labor expenses, the mail agency sustained an operating loss of $2.4 billion for the past fiscal year, lower than the previous year.Congress also has stymied the service's efforts to close some post offices in small towns. Under the new plan, mail would be delivered to homes and businesses only from Monday through Friday but would still be delivered to post office boxes on Saturdays. Post offices now open on Saturdays would remain open. Over the past several years, the Postal Service has advocated shifting to a five-day delivery schedule for mail and packages â¿¿ and it repeatedly but unsuccessfully has appealed to Congress to approve the move. An independent agency, the service gets no tax dollars for its day-to-day operations but is subject to congressional control. The proposed change is based on what appears to be a legal loophole â¿¿ and that may be a gamble. Congress has long included a ban on five-day-only delivery in its spending bills, but because the federal government is now operating under a temporary spending measure rather than an appropriations bill, Donahoe says it's the agency's interpretation that it can make the change itself. "This is not like a 'gotcha' or anything like that," he said. The agency essentially wants Congress to keep the ban out of any new spending bill after the temporary measure expires March 27. Might Congress try to block the idea? "Let's see what happens," he said. "I can't speak for Congress."