NEW YORK (CNN/Money) - Neither rain, nor sleet, nor snow is supposed to stop mail deliveries, but costs are starting to force trimming of some operations within the U.S. Postal Service.

The Postal Service has started reducing the hours at some of its lesser-used post offices as it faces dwindling first-class mail deliveries, the Wall Street Journal reported Tuesday.

About half of the post offices in Maine have already scaled back their hours during the past several months. The Postal Service is implementing similar moves in Vermont and upstate New York, and is considering a series of national cutbacks, the paper reported.

The Service says it hasn't set a target for the number of hours it will trim nationwide, but it is looking to cut hours when few customers are in its offices.

"We are trying to squeeze out what we don't have to spend while maintaining the service that people want," a Postal Service spokesman told the Journal.

The cutbacks are the latest in a series of moves under Postmaster General John Potter since he took the job in mid-2001. Since then, the service has trimmed 47,000 full-time jobs, or 6 percent of its work force, through attrition, according to the paper.

In addition, the Service has recently closed, or will close, 566 post offices across the country where service has already been suspended, the Journal reported.

One example of an office closure is the Fort Lyon, Colo., post office, which used to be housed in a veterans' home, but was shut down after the home converted into a prison, according to the paper.