Proposed provincial legislation, known as Bill 3, calls for a 50-50 split between municipalities and unionized workers on pension contributions and deficits.
Firefighters blocked the main access to the Port of Montreal and there were also demonstrations in subway stations.
In Quebec City, municipal employees tried to prevent city buses from leaving a garage. There was also a protest at the site of a new $400-million amphitheatre that is under construction.
Another demonstration outside Montreal city hall took place as Mayor Denis Coderre presented the 2015 budget.
In August, the council chamber was overrun by about 250 unionized workers who barged in, tossed papers, threw glasses of water and smashed windows.
Coderre continued to defend of the legislation tabled by Premier Philippe Couillard's Liberals, saying it was a necessary measure.
"We have given our support to this bill because we are convinced the solution to the swelling costs of pension plans does not go through taxpayers' pockets. . .the solution comes through negotiations with our union partners," Coderre said on Wednesday.
In the past, there were more people working to pay for pension plans, Coderre said.
"Now, more and more, it's the opposite," he added.
The province-wide demonstrations, which involved about 25 unions, were generally peaceful. A brick was reportedly thrown through the window of the Montreal-area riding office of Quebec Municipal Affairs Minister Pierre Moreau, who is spearheading the legislation.
"The problem is that you have a $3.9 billion deficit over those pension plans and they want people to pay for those deficits which is not fair," Moreau told reporters in Quebec City.
"And people who don't have a pension plan — why would they pay for a deficit that doesn't belong to them?"
Moreau also said an agreement had been reached with the opposition Parti Quebecois which would allow Bill 3 to be approved next week.
But Marc Ranger, a spokesman for a union coalition, said municipal workers will continue to put on the pressure.
"We could sit down and just cry and let that piece of legislation go through, but No!," he told reporters outside Montreal city hall.
"When you have something that is going on that is unfair, well, we won't let that happen."
Unions say they are being blamed for pension deficits that are not of their making and feel some municipalities are looking to save on labour costs by renegotiating retirement deals.
Employees like police officers, firefighters, public transit and other blue- and white-collar workers have been dressing down for weeks, wearing funky pants as well as plastering stickers over their vehicles.
Montreal police, for example, have donned bright red ball caps and shed their work-issue slacks for camouflage, fluorescent and multi-coloured pants to show their anger.
The pension battle is a test for the Quebec Liberals who warned when they came to power last April that tough economic decisions would be coming.
— With files from Peter Rakobowchuk and Pierre Saint-Arnaud in Montreal and Martin Ouellet in Quebec City.
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