Four workers in the United States have lost their jobs after refusing to take a test to see if they were smokers.
Weyco says it is proud of its stance on smoking
They were employees of Michigan-based healthcare firm Weyco, which introduced a policy banning its staff from smoking - even away from the workplace.
The firm says the ban is to keep health costs down and has helped 14 staff to stop smoking, but opponents say the move is a violation of workers' rights.
If the firm survives a potential legal challenge, it could set a precedent.
Weyco gave its staff a stark ultimatum at the end of last year - either stop smoking completely on 1 January or leave their jobs.
The four workers who refused to take the test left their jobs voluntarily, although a lawyer for Weyco confirmed the company was preparing to dismiss them.
The firm says that, as its business is to help other firms save money and improve employee health through its benefit plans, it is only natural it should take a lead on the issue.
"For every smoker who quits because of it, there will be many people - family members, friends, co-workers - who are very thankful the person won't be going to an early grave," said Weyco President Howard Weyers, in a message on its website.
But opponents say it is a violation of workers' rights to indulge whatever habits they choose to when they are off-duty, particularly as smoking is legal and does not impair people's ability to do their jobs.
According to Reuters news agency, Mr Weyers wants to turn his attention next to overweight workers.
"We have to work on eating habits and getting people to exercise. But if you're obese, you're (legally) protected," he said.
The BBC's Jannat Jalil in Washington says that if the firm survives any future legal challenges, it could set a precedent for other companies to follow suit.
"Certainly it raises an interesting boundary issue," job placement specialist John Challenger told Reuters. "Rising healthcare costs and society's aversion to smoking versus privacy and freedom rights of an individual."