ST. PAUL (AP) -- Anthrax testing scheduled for Wednesday at a St. Paul dead letter office that handles undeliverable mail from other states has been delayed.

Testing is planned for the site because it is one of three centers in the country where undeliverable mail goes to be sorted.

Mail from about 20 states goes to the one-story St. Paul building -- including envelopes and packages from New York and New Jersey, where anthrax has been found.

Testing was delayed because the testing crews were running behind on another project, said Jim Ahlgren, spokesman for the Northland District of the Postal Service. No time or date has been set.

"It's all a precautionary thing," Ahlgren said.

But he acknowledged that in light of recent events, it was the "prudent thing to do" to make sure postal workers were safe.

About 80 employees work at the plant, processing about 80,000 pieces of mail per day, plus about 30,000 parcels per week.

Jim Beaupre, a St. Paul representative for the American Postal Workers Union, said he's angry that the testing was delayed. He hadn't been told yet by Postal Service officials when a reporter called him.

"They won't communicate at all with us on what we consider matters of life and death," he said. "As a postal worker, I'm very upset and very angry about it."

He thinks there's a "very strong possibility that there's anthrax there" because it handles undeliverable mail from the East Coast.

Anthrax attacks have killed four people as of Tuesday, including two postal workers.