The union representing Tom Hunse wants him fired. The leadership does not approve of his part-time job and has petitioned the City of Toronto to terminate the 20-year veteran firefighter.

The offending part-time gig? Fighting fires. When he is not working at Station 422 in Toronto's west end, Mr. Hunse answers calls with the volunteer force that serves Innisfil, Ont., and the surrounding communities.

He is what is called a "double-hatter" – a professional firefighter who works part-time for a volunteer force on his days off. Volunteer firefighters are not obliged to respond to calls, and are paid by the hour when they do.

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Firefighter union bylaws prohibit double-hatting, but the mayors of many small Ontario towns say it is necessary. Even though Ontario relies on volunteers – perhaps more than any other province – it is one of two jurisdictions in Canada where a firefighter's right to volunteer is not protected by legislation. (Newfoundland and Labrador is the other.)

Mr. Hunse, a 50-year-old father of two, is at the centre of a legal battle that could change the face of emergency services in bedroom communities across the province. He could lose his job and his pension. The City of Toronto has so far declined to act on the union's request to have him dismissed, but the issue is scheduled to go into arbitration in October.

Mr. Hunse is challenging the union's conduct before the Ontario Labour Relations Board.

"I'm just standing up for what's right. Why should the union be able to tell me what I can or can't do when I'm not at work?" he said in a recent interview in the backyard of the Victorian farmhouse where he lives, in Cookstown, an hour's drive north of Toronto.

No one knows how many double-hatters Ontario has – most are quiet about their off-duty work for fear of provoking union leaders – but it is estimated there are hundreds among the 19,000 men and women who take time off their regular jobs to respond to fires, crashes and medical emergencies in small communities.

Five double-hatters were working for the town of Innisfil when a complaint was filed in 2010. Four years later, Mr. Hunse is the only one left fighting for the right to volunteer.

Double-hatters take part-time jobs from young people trying to get into firefighting, said Frank Ramagnano, a spokesperson for the Toronto firefighters union. Many municipalities have wait-lists to become volunteer firefighters, and people looking to break into the profession get important experience on volunteer forces.

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Double-hatters are also problematic in that they answer to two fire chiefs, presenting a risk in the event of a natural disaster or major catastrophe in which both forces call them in, he said.

"Can you be a member of the Liberal and Conservative party at the same time? You can only be a card-carrying member of one. Our constitution is if you're a full-time member, you're our member."

Small town mayors across the province are following Mr. Hunse's case closely. The Association of Municipalities of Ontario and the town of Innisfil have both applied for intervenor status.

In the 11 years he has been mayor of Tecumseh, Gary McNamara said he has seen a dozen double-hatters pressed into leaving the volunteer force for the community of 25,000 near Windsor, in southwestern Ontario.

The town gets 300 to 350 calls for assistance each year, and most are for medical help or car accidents. Mr. McNamara said he would have to raise taxes as much as 20 per cent to afford a full-time force.

"The double-hatters, all they want to do is protect their friends and families in their own communities, so why can't they?" he said. "They are the backbone of small town fire services. This is a public safety issue."

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The issue has made headlines in Ottawa, Stratford, Orangeville and elsewhere as double-hatters have been forced to ignore calls for help in their local communities, or resigned in large numbers after union pressure.

Mr. Hunse, with the support of his wife, Brenda, has refused to cave in to the pressure to resign. He carries a pager on his days off, and attends calls when he can. He makes only about $3,000 a year – but considers the farmers, carpenters and local business owners he volunteers with close friends.

He has lost sleep over the possibility of losing his job, but said he does not know how to back down.

"Why should I sit at home when my neighbour's house is on fire?" he said.