The U.S. Postal Service's plan to close 252 mail processing facilities and cut 28,000 jobs by the end of next year faces big obstacles.

Deciding which plants to close will be difficult and likely inspire intense opposition from communities. Actually closing them could take a year or longer, and most workers whose jobs are eliminated will stay employed under union rules.

Most of the job cuts will come from attrition and retirements, not layoffs, while remaining workers get shuffled into new locations and positions.

Postal officials say they can save $3 billion by 2015 by getting rid of buildings, running equipment more efficiently, operating fewer mail trucks and cutting employees. The cuts are aimed at helping the agency avert bankruptcy after years of red ink and declining mail volume.