(Hueytown, Alabama - Associated Press) - A chemical used to make artificial fishing lures leaked from a flimsy package at a post office and sent about 20 postal workers to a hospital Tuesday after some experienced breathing problems, authorities said.

The noxious yellow liquid was so highly concentrated that it damaged the tile floor when it spilled, Police Chief Doug McBee said

Six postal workers had trouble breathing and were taken to UAB Medical West in nearby Bessemer for treatment and decontamination. More than a dozen others were taken to the hospital as a precaution, postal officials said.

The source of the package was not immediately confirmed.

“The hazardous materials people say it’s fish bait, but we want to make sure our employees are safe,” said Larry Dingman, a spokesman for the U.S. Postal Service in Memphis, Tenn.

The single-story brick post office, located a few miles west of Birmingham, was evacuated.