House lawmakers included the provision in a broad spending bill they approved Thursday in a 52 to 43 vote.
Under the proposal, state employees would have to pay 20 percent of their health insurance premiums. Sponsors say it would not impact the current two-year contract negotiated by Gov. Terry Branstad and state workers that says workers won't pay anything toward health care premiums.
Danny Homan, president of Iowa Council 61 of the American Federation of State, County and Municipal Employees, says he thought the measure would be illegal if it became law.
The policy will likely be rejected by the Democratic-controlled Senate, where the legislation now goes.