Quebecor locked out employees at its newspaper printing plants in Mirabel on Tuesday morning.
That location is used to print the daily French-language newspapers Journal de Montreal and Le Devoir.
Stephane Lacroix of Teamsters Canada said he was surprised by the lockout because he felt progress was being made during negotiations for a new collective agreement.
"There are so many contradictory messages in what they're saying that it makes no sense," Lacroix told Radio-Canada.
The lockout affects 125 employees including press operators, mechanics, and electricians, about 50 of whom have been laid off in recent months.
In a statement, Quebecor said months of negotiations have failed to reach a new contract, so it had no choice but to lock out employees while applying for a new mediator to work out an agreement.
The company has a history of lockouts in Quebec, once locking out journalists at Journal de Montreal for two years.
Quebecor is controlled by Parti Quebecois leader Pierre Karl Peladeau, who has repeatedly promised to put his shares into a trust, but has not yet managed to do so.
