FREEPORT, Maine – Fire chiefs and lawmakers are working to protect the system of volunteer firefighting that has served rural America for more than a century but is threatened by an ambiguity in President Obama's health care law.

Small and rural fire departments from California to Maine, which has one of the country's highest percentages of volunteer and on-call firefighters, rely on volunteers to avoid the cost of paying them to be on duty between fighting fires.

The volunteers are considered employees for tax purposes, a classification that grew out of an ongoing effort to attract firefighters by offering them such incentives as stipends, retirement benefits and free gym memberships.

That leaves open the question of whether the volunteer firefighters fall under the health care law's requirement that employers with 50 or more employees working at least 30 hours a week must provide health insurance for them. Fire departments say they can't afford to pay such a cost.

Volunteer fire departments from Virginia to Connecticut to Florida are wrestling with the issue. In Minnesota, 97 percent of fire departments are fully or mostly staffed by volunteers, according to the 2012 National Fire Department Census.

Most volunteer departments operate "on a shoestring budget — holding pancake dinners to raise money to put enough gas in the truck so they can respond to the next fire," said Dave Finger of the National Volunteer Fire Council.

Faced with the cost of insurance, or being fined if they do not provide it, departments would likely be forced to reduce the number of hours firefighters can volunteer or eliminate the benefit programs.

That has both fire chiefs and lawmakers worried.

Darrel Fournier, fire chief in Freeport, a town of about 8,000 people in southern Maine, said his department is bracing for what could be significant costs under the health care law. He expects he'll have to provide coverage for the five firefighters he employs part time. That would cost the city — and ultimately taxpayers — about $75,000, or a penalty of $150,000.

Additionally, in a busy winter with lots of fires, emergency calls and accidents, he said his roughly 50 volunteers could work more than 30 hours a week, meeting the threshold under the law that would require him to provide health insurance for them as well.

To avoid the penalty, Freeport could cut back on the hours part-time and volunteer firefighters work, but that would mean finding more volunteers to make up the difference.

The question is expected to be answered when the Internal Revenue Service releases final regulations this year before the provision takes effect in 2015. A Treasury spokeswoman said the department is taking the concerns into account as it works toward the final regulations but wouldn't comment on what they're likely to include.

In the meantime, Maine's U.S. senators are backing a recently introduced bill aimed at ensuring volunteer firefighters and other emergency responders are exempt from the health care law requirement.

"This is yet another adverse and unanticipated impact of Obamacare," said Maine Republican Susan Collins.

It's too early to ring the alarm, concluded Trish Riley, an adjunct professor of health policy at the University of Southern Maine's Muskie School of Public Service.

"With any major piece of legislation like this, there are bound to be unintended consequences," she said. "But you can't leap to conclusions before the federal government has the opportunity to address it."

Finger said he's confident the issue will be addressed either through the regulations or legislation and is urging fire departments to avoid taking any immediate steps.

But he realizes that the political tension over the health care law means that even a small change can turn into a big fight.

"The tough part is, anything having to do with this law is just so partisan that it's difficult to take action on," he said.