But now, they could cost a handful of General Motors line workers their jobs. The workers were allegedly filling envelopes with baby powder and leaving them for co-workers to find.

GM cracked down in two separate anthrax hoaxes.

The first happened at the Flint truck and bus plant on Monday. There, four workers remain indefinitely suspended without pay.

The second happened Wednesday where one line worker was fired after a incident at a plant in Wentzville, Mo.

In Flint, a second shift assembly line worker found the suspicious, powder-filled envelope inside a full-size, pickup cab.

He got his boss, who called security who then called the Flint Police Department. They quarantined the truck and in short order figured out the fake anthrax was baby powder. After questioning, one worker admitted involvement Monday night. On Tuesday, three others came forward.

According to the local UAW contract, this offense can result in firing. Flint police are still weighing whether to arrest the workers.

In Wentzville, a worker pulled out his newspaper on break and a suspicious envelope fell out. It, too, contained powder.

Police and hazmat units got the call and a fellow line worker admitted to putting the baby powder in the envelope. The worker said it was a joke.

Police arrested him and GM fired him on the spot.

GM spokesman Dan Flores said that the company is taking these hoaxes very seriously.

"While they may have had fun in mind, now is not the time for this kind of biological hoax," Flores said. "Employees who participate in anthrax-related scares will be disciplined in a severe way," he said.

What's more, the United Auto Workers union is supporting GM in its stance.

In Flint, GM's plant manager and the union local president sent a letter to every worker telling them under no uncertain terms that this is no time for trick or treat.