Thirty-two members of the Chicago Fire Department’s brass resigned their exempt positions Monday and returned to rank-and-file status in a fight over pay and benefits that will cost taxpayers hundreds of thousands of dollars.

The bosses will return to their career service ranks of battalion chief and, in one case, paramedic field chief, but will continue to “act up” in their exempt positions.

That means the 32 will now be eligible for overtime, holiday pay, duty availability, hazmat and other forms of supplemental and specialty pay afforded to members of the rank-and-file.

They resigned en masse at 8 a.m. Monday. They represent more than half of the brass on the fire suppression side of the Chicago Fire Department but just one of roughly a dozen bosses overseeing emergency medical services.

The highest-ranking member is First Deputy Fire Commissioner Richard Ford II. Others include Mark Nielsen, deputy commissioner of the Fire Department’s Bureau of Operations, Michael Callahan, who oversees logistics, and Don Hroma, district chief of training.

Earlier this month, the Chicago Sun-Times reported on the behind-the-scenes struggle for pay and benefits that threatened to create a fire department leadership vacuum.

The fire officials are seeking pension changes, expanded health insurance benefits and pay raises — and have been unable to persuade Mayor Rahm Emanuel and Fire Commissioner Jose Santiago to sweeten the pot for them. City officials say that would require a change in the state pension code.

“The city continues to have conversations with those exempt fire department staff who have expressed concerns about the state pension code, which is pending Springfield legislation,” said Julie Kaviar, a city spokeswoman.

Fire officials must retire at age 63. But exempt officials — non-union, senior staff — must pay for their own health insurance until they hit 65. Exempt fire officials also lose pay perks, including vacation time, when they become exempt staff members.

In addition, the state pension code doesn’t allow exempt fire officers to earn pension benefits based on their current salary. Instead, their pension benefits are based on the lower salary of their most recent union-covered job.

All of that can result in a loss of thousands of dollars in pay each year for exempts — sometimes $20,000 or $25,000, sources say.

Pending state legislation known as a “brass bill” would allow exempt fire employees to earn a pension based on the pay for their current jobs.

One city source said Santiago was sympathetic to the exempt officers’ concerns, despite being unable to help.

Some rank-and-file members questioned why Emanuel didn’t just let the bosses quit and replace them instead of allowing them to return to their career service ranks in an arrangement with the potential to cost Chicago taxpayers a fortune.

But a source familiar with the resignations said that kind of ultimatum would be easier said than done.

“It’s hard to get people to serve as exempts because, as soon as they cross over, they lose money,” the source said.

As for the mass resignations, the official argued that the Fire Department brass had no other choice. All 32 exempts are closing in on the mandatory retirement age of 63.

“Most of the people in this group are up against the wall. They have to self-demote two-to-four years before they retire to rebuild their pension before turning 63,” the source said.

“The collective bargaining agreement has improved over the years for the rank-and-file, but it has not improved for the exempts. In private industry, when the rank-and-file gets something, the bosses also get something. That hasn’t happened in the Fire Department. Some of these guys have lost in excess of $25,000. That’s rather insane.”