"Breathing mist from metalworking fluids can cause severe respiratory ailments," the unions said in a joint statement.
NIOSH has found "substantial evidence that metalworking fluids cause cancer of the larynx, rectum, pancreas, skin, scrotum and bladder," their statement said.
In 1998, NIOSH recommended a standard for factory workers' exposure to oil-based metalworking fluids ten times lower than the current OSHA standard, set in 1971.
The unions first petitioned OSHA for a new metalworking fluids standard in 1993.
The agency has issued a set of guidelines for working with the fluids, but decided against new rules for exposure.
"This is an egregious example of a public rulemaking process that has been obstructed by backroom industry lobbying," United Steelworkers President Leo Gerard said in the statement. OSHA must "stand up to the industry lobbyists who don't care how many workers suffer from exposure to metalworking fluids," he added.