A bioterrorism scare slammed the brakes on New Haven’s mail delivery system Friday, foreshadowing a series of terrorism scares Monday.

White powder, which later tested negative for anthrax, was found in mail bins by post office employees at the main New Haven post office, located at 50 Brewery St. The courier center halted all of its operations and evacuated the building just before 9 a.m. — two hours after workers discovered the powder.

Initial on-site tests showed no presence of anthrax in the substance, but FBI representative Lisa Bull said that more extensive test results from the FBI state office have not yet come in.

Officials do not know the source of the powder.

A number of suspicious packages and powders have been reported to New Haven and state authorities in the past week, including as many as six Monday.

Friday’s scare stopped operation of New Haven’s main post office from nine in the morning to four in the afternoon. Service to three metro-area zip codes — 06510, 06519 and 06511 — was delayed. Approximately 22,000 homes and businesses were affected.

Postal Workers’ Union President John Dirzius said grime in mail bins is not uncommon, but the increased caution is appropriate.

“Two months ago, we probably wouldn’t have done anything,” Dirzius said. “The heightened security has added to people’s sensitivity.”

The Postal Workers’ Union is currently demanding gloves for its mailroom employees as part of a national call for increased sanitary precautions.

“Our concern is the safety and health of our employees,” Dirzius said. “We handle millions of pieces of mail a day.”

A warning issued by the FBI a day before the scare prompted calls to civil agencies around the country and state.

Bull said there have been over 100 reports of suspected biological threats in Connecticut since the Sept. 11 terrorist attacks. She added that the extent to which citizens should be concerned depends upon the nature of the situation.

Since the FBI’s warning of the possibility of further terrorist activity, post offices and businesses have kept their eyes open for suspicious packages.

On campus, Yale Station is continuing to scrutinize incoming mail. Officials at the post office encourage students who receive unusual mail to notify authorities.

Yale Station mail clerk Ward Colburn said, “Our effort is ongoing year-round, terrorists or not.”

To date, Yale Station has not received any reports of suspicious mail.

“We are continuing same as always, although a little more aware,” added Colburn.