A spokesman for a union coalition said Municipal Affairs Minister Pierre Moreau wants to make municipal workers poorer and is "ripping up contracts."
Five days of hearings on Bill 3 wrapped up Tuesday with the government standing firm on several pension-related issues.
The proposed legislation calls for a 50-50 split between municipalities and unionized workers on pension contributions and deficits.
It would also allow municipalities to temporarily suspend cost-of-living hikes.
The Liberal government argues the pension plans of municipal workers carry a collective deficit of about $3.9 billion and aren't sustainable in the long term.
Unions peg the shortfall at $2.2 billion.
They say they are being put on the hook for pension deficits that are not of their making and feel some municipalities are looking to save on labour costs by renegotiating retirement deals.
Coalition spokesman Marc Ranger said a march will be held Sept. 20 to reinforce their opposition to the legislation, which Moreau hopes will become law this fall.
"It's not by eroding our labour conditions that they're going to improve the lot of all Quebecers," said Ranger.
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 Premier Philippe Couillard's Liberals, who warned when they came to power last April that tough economic decisions would be coming.