The United Auto Workers and the International Association of Machinists and Aerospace Workers both allege that Peoria, Illinois-based Caterpillar violated the terms of their contracts by unilaterally banning smoking on the company’s property. The unions, which filed their charges separately, say employees have had the smoking privilege detailed in their contract for 60 years.

Employers have been increasingly willing to engage with employees—and now unions—in a battle that pits the right to smoke versus the health and financial costs of doing so. A number of employers have already made smoking, on or off the job, an offense that could lead to termination.

Whirlpool Corp. in Evansville, Indiana, recently suspended 39 workers who lied about their smoking habits on health insurance forms to avoid paying more on their health care premiums. Johnson & Johnson faced grumbling employees when the company outlawed smoking on its property more than a year and a half before Caterpillar.

While labor unions are fighting Caterpillar’s anti-smoking policy, the heavy-machine manufacturer may have state law on its side. Caterpillar’s new policy comes six months after Illinois enacted a law that bans smoking in the workplace. The law makes it illegal to smoke inside buildings and within 15 feet of office entrances, exits and ventilation ducts.

Union officials say Caterpillar’s ban goes further than state law. The company has prohibited smoking anywhere on its property regardless of how close a person is to a building. Such a policy change must first be agreed to through collective bargaining, a lawyer representing the UAW says.

“There’s a legal obligation that the union is seeking to uphold and vindicate,” says Stanley Eisenstein of Chicago-based firm Katz, Friedman, Eagle, Eisenstein, Johnson & Bareck.

Caterpillar spokeswoman Rachel Potts would not comment on the charges except to say the company “is committed to creating and maintaining the safest and healthiest work environment.”

Eisenstein says the union filed a second charge June 2 after at least one union worker was suspended indefinitely for violating the company’s no-smoking policy. Eisenstein says the union believes its workers are being unfairly targeted for violating the smoking ban.

Will Vance, an official with the National Labor Relations Board in Peoria, says the agency will determine whether the company implemented the smoking ban to comply with state law or if it constituted a change in work conditions without consulting the union. He expects the board to respond to the charges by the end of June.