Work has stopped at about half of the city of Montreal's construction sites as municipal engineers go on strike.

Engineers, scientists, researchers and veterinarians - all members of the SPSPEM union - walked off the job on Tuesday, and they protested at Mont Royal metro and at construction sites along St. Denis St. early Tuesday morning, then began marching to Montreal City Hall in mid-morning.

Once there, they used a tamper to destroy hard hats, as a symbol of what they say is the city's refusal to rely on their expertise.

The union of applied science professionals, which represents 440 engineers, researchers, veterinarians and surveyors, says the city is asking for pay cuts at a time when it should be relying on their expertise to stop corruption.

Union vice-president Gisella Gesuale says the city is asking for a 9 per cent salary cut, and $12 million in concessions.

"We've been at the negotiation table for five years, but unfortunately we're at an impasse with Mayor Coderre. He's not willing to move," said Gesuale.

She added that if Coderre was serious about fighting corruption, he would be doing his best to make sure city engineers can do their jobs properly.

"Like the Charbonneau Commission said, it's important to keep the internal expertise inside within the company in order to reduce corruption," said Gesuale.

The SPSPEM members have not had a contract since 2010.

City engineers are responsible for supervising construction and doing quality control on all municipal construction work.

With them off the job about half of the construction sites in the city of Montreal have gone silent, since the work being done cannot be verified.

"We feel bad for Montrealers. This wasn't our objective. We didn't want to affect traffic or anything of that sort. It's been five years and he put us against the wall so this is our only option," said Gesuale.

"We apologize to Montrealers."

Sites now paralyzed include construction at Atwater Ave. and Sherbrooke St. and the massive water-and-sewer work on Cote-des-Neiges Rd. near Cedar Ave.

Essential services are guaranteed, but the union said it’s in it for the long haul, if required.

“There will be a time we’ll try to prevent scabs from working, and we’ll visit construction sites,” warned union president Andre Emond.

The city of Montreal issued a statement "regretting" the strike and saying it was disappointing the union did not attend this past Friday's negotiation session.

“We could not come to an agreement but we just hope we can resolve these issues more rapidly,” said Montreal Executive Committee member Pierre Desrochers.

The opposition argues the mayor allowed the conflict to simmer far too long.

“It's going be bad for tourism, it's going to be bad for the economy it's bad for Montrealers that have to get around, so we need Mayor Coderre to start rallying and to get to the table and get this negotiating going, so we can get a good bargain and get going,” said Projet Montreal councillor Craig Sauve.

The union represents 440 engineers, researchers, veterinarians (the three who work at the Biodome) and surveyors.

“If there's anything wrong with the animals we're going to be there as soon as possible to fix the problem,” said Gesuale.

The strike does not affect work being done on provincial or federal job sites.