Montreal Mayor Denis Coderre is at odds with the city's firefighters' union over his impromptu appearances at fires and other emergencies around the city.

Union officials say it's not appropriate for Coderre to use fires as photo-ops yet treat firefighters poorly.

This week, union president Ronald Martin published an open letter condemning Coderre for his support of proposed provincial legislation that would see municipal workers and cities evenly split the cost of the $4-billion municipal pension plan deficit.

Ronald said Coderre is no longer welcome at the scene of fires around the city, which the mayor has at times attended in ceremonial firefighter's gear.

Martin asked Coderre to return the uniform, saying he is no longer fit to wear it.

Coderre replied to the union via Twitter on Thursday to say he expected the firefighters to act professionally and occupy themselves with helping victims.

Current retirees could have indexed pension increases put on hold under the proposed legislation, known as Bill 3.

When the proposed legislation was announced on June 13, 80 Montreal firefighters decided to take early retirement all at once to protect their pensions.

The mayor can’t say he supports both collective agreements and Bill 3, Martin said in his letter.

Martin said the new law would put too much financial pressure on firefighters and other city employees to make up for municipalities’ pension plan deficits, and that they would end up losing quite a lot of money.

Montreal firefighters already make less compared to their colleagues in other cities around Quebec and Canada, and Martin said Bill 3 would add insult to injury.

“Firefighters feel had, they feel abandoned by Coderre and his support for this law,” Martin said.

The union can’t stop Coderre from showing up at fires, and Martin said firefighters will remain civil and professional with the mayor.

But they wanted to send a message to the mayor.

"The firefighter's uniform symbolizes our absolute confidence in each other — we need that when we go into a burning building. When the mayor shows up in that same uniform, it's an insult to that confidence. And we wanted to send a clear signal," Martin said.