The Montgomery County Council approved an ambulance fee in a 6 to 3 vote Tuesday, reviving the only county law to be struck down by referendum.

The fee would be charged to patients for ambulance service, but it would be paid for by health insurance in most situations. People without health insurance and people below a certain income threshold would be exempt from the fee. County officials stress that county residents would neither see a bill nor incur out-of-pocket expenses.

But volunteer firefighter groups say they oppose the fee partly because it would make residents hesitant to call for assistance. They added that county officials should not resurrect an issue on which voters have already decided.

Some county officials believe that the volunteer firefighters will start another referendum campaign. Eric N. Bernard, executive director of the Montgomery County Volunteer Fire Rescue Association, said all options are open.

By enacting the legislation, the county again joins the vast majority of local jurisdictions that have the fee. Prince George’s, Fairfax and Prince Williams counties have similar fees, while Calvert, Loudoun and Howard counties do not.