But some worry that employers wading into the realm of prescription drugs could infringe on privacy and dredge up stereotypes about people who take certain medications.

“People make stereotypical assumptions about certain medications, whether they’re prescription or over-the-counter, and use those prejudices from prohibiting people from maintaining gainful employment,” said Nick Pladson, an Equal Employment Opportunity Commission lawyer in Minneapolis who is suing a manufacturing company on behalf of a man who was required to disclose the prescription drugs he was taking and was later fired.

Although Dura officials said in court documents that the goal of expanded testing was to protect employees, some plaintiffs in the lawsuits claim they were injured on the job and supervisors knew about the medications they were taking. Others say they believe the company wanted to get rid of them because they were costing it thousands of dollars in insurance premiums, a charge the company has denied.

“The reason I was taking the medication was a work-related injury,” said Mark Long, 38, who worked at Dura and was fired for taking hydrocodone. “I really didn’t expect for my job to end.”

Supervisors worried that employees, who manufactured hundreds of thousands of windows for automotive companies including General Motors and Ford within very close proximity of one another, could cause a “domino effect” if one was impaired and had an accident.

Mr. Long said he had stopped taking Lortab after losing his job because the pain subsided when he was not working full-time. With work scarce in Lawrenceburg, a city of 14,000 in south-central Tennessee, Mr. Long drives 70 miles each way to work as a boat mechanic in northern Alabama.

Mrs. Bates, whose job was trimming car window molding, said she had been unable to find another job. She said she understood Dura’s safety concerns but believed the company should have worked with employees who take prescription drugs rather than fire them.

“If the medicine they’re taking is not good for them or the workplace, then there should be some sort of program where they can teach us how that affects you or see if something else can be worked out,” Mrs. Bates said. “But that was not an option for us.”