Combining the Frederick and Baltimore operations for the rest of the summer is being considered for efficiency.
Postal Service spokeswoman Freda Sauter wrote in an e-mail that the proposal is part of a nationwide study of mail volume and capacity.
The Postal Service, which doesn't receive tax money, has a year-to-date net loss of $2.3 billion, while mail volume is down 7.5 billion pieces, her e-mail said.
At the Frederick processing center, the drop from a year ago is about 10 percent to 15 percent, Wall said.
"A significant portion of the losses can be attributed to an unprecedented decline in mail volume due to the economic recession and longer-term financial pressures, such as the diversion of letter mail to electronic alternatives," Sauter wrote. "The Postal Service will continue to look for ways to be more efficient which include looking at our transportation networks.
"At this time, trucks leaving the Frederick P&DF with outgoing mail ... are only half full. In Baltimore full truckloads are sent through the network, reducing the number of trucks used and saving fuel .... When (the) fuel price goes up 1 cent it (costs) the postal service $8 million annually."
The Postal Service is expected to decide in the next few weeks about the trial, which would last until Labor Day, Sauter's e-mail said.
Wall said trucks run daily between the Frederick and Baltimore centers and the change wouldn't affect how long it takes local mail to be delivered.
John Munson of Maugansville, a retired postmaster, said he doesn't believe it.
Munson said he and his post office colleagues occasionally tested that theory by mailing letters to themselves on weekdays and weekends. Mail processed in Baltimore generally took longer to come back, he said.
Munson also disputed the merger would be temporary. He said he believes if Frederick processing moves to Baltimore, it will stay there.
Munson said he supervised mail processing when it last was in Hagerstown, in 1977, then stuck with the operation when it moved to Frederick the next year.
He also was a postmaster in Middletown, Md., and in Cascade.
The Frederick Processing & Distribution Facility has about 200 employees, including mail handlers, clerks and maintenance workers, Wall said.
Asked if switching to Baltimore would mean layoffs, Wall said summer staffing usually is lighter because mail volume is lower, so employees take vacations then.
The move could save money by cutting the need for overtime in Frederick, he said.