NEW YORK, Dec. 30 (UPI) -- A test conducted just a few days ago detected a remnant of anthrax at the Postal Service's huge Morgan Processing Center, reinforcing fears of some New York postal workers that they are still in jeopardy -- although postal officials repeated Saturday the new finding did not represent a serious health threat.

The apparent leftover trace from previous contamination was discovered in a piece of equipment among several previously tested, found to be harboring the anthrax spores and cleaned.

Postal service officials repeated the facility will not be closed. No postal workers at the Morgan facility have become infected but two postal workers elsewhere have been among the five anthrax fatalities.

The development increased pressure on reluctant postal workers to follow the advice of the Centers for Disease Control and Prevention and be administered an anthrax vaccine not approved by the Food and Drug Administration.

"The U.S. government and the U.S. Postal Service are using postal workers as guinea pigs by making available the anthrax vaccine that isn't even approved by the federal Food and Drug Administration," New York Metro Postal Union president William Smith told United Press International Friday.

"We've had at least 54 calls from (military) veterans or family members who said they have been injured from taking the vaccine. It's outrageous," he said.

Several letters contaminated with anthrax went through the Morgan Processing and Distribution Center in Manhattan and several mail sorting machines then tested positive for anthrax. The postal union sued the federal government to have the nation's largest mail processing center closed until the machines were cleaned and the entire building was tested.

The union lost that case but is preparing to go to U.S. District Court in Manhattan in February because they believe anthrax may still be a threat. Reinforcing that fear is the fact the anthrax vaccine is being made available as well as another 40 days treatment with the antibiotic Cipro.

None of the 7,000 postal workers with access to the Morgan Center have contracted anthrax.

"If there was no problem why do they keep the building open and give everyone 60 days of Cipro and now that those 60 days are over make the vaccine available and give more Cipro?" Smith said.

Federal officials have made the vaccine available to those exposed to anthrax-contaminated buildings in New York, New Jersey and Washington but they have not made any formal recommendation on whether to take the vaccine.

"We are giving an enormous amount of information to workers that may have been exposed," Susan Brennan, U.S. Postal spokeswoman in Washington, told UPI. "However, we are not advising the employees and we say that they make the decision to take the vaccine on their own with consultation with their physician."

According to Brennan, postal workers have three options: take the three-dose anthrax vaccine, take another 40 days of Cipro or watch for any anthrax-related symptoms.

"The reason the federal government said it could not close the Morgan Center was that their medical expert said in court that after 40 days the chance of contracting anthrax was greatly reduced and now they're telling us 'Here's the vaccine and here's another 40 days of Cipro,'" Smith said.

The vaccine, which was given to the military during the Gulf War, has never been given to people already exposed to anthrax, according to Smith.

The Postal Service confirmed that fewer than a dozen of New York, New Jersey and Washington postal workers have decided to take the vaccine since it was made available Thursday, but the workers have until Jan. 7 to decide on whether to take the vaccine.

"Postal workers feel used and abused by the federal government and the president and the Congress know it," Smith said. "A lot of workers stopped taking Cipro because of the side effects and there are hundreds of temporary postal workers who don't have health insurance so they have no physician to consult."