Despite being "disappointed and bitter" at having the legal right to strike suspended, leaders of Quebec's construction unions say workers will don their tool belts and obey back-to-work legislation.

"We are asking workers to respect the law – to respect it in its entirety," Yves Ouellet, spokesman for the alliance of construction unions, said on Monday. "Just don't expect them to do it with smiles on their faces."

That means work will resume on Tuesday morning on institutional, commercial and industrial sites across the province, ending a two-week walkout.

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The law includes stiff penalties for any party that stages a strike or lockout, including $100 to $500 daily for individual workers, $7,000 to $35,000 a day for union leaders and employers, and up to $175,000 daily for unions or construction associations.

Quebec's National Assembly staged a rare long-weekend sitting to impose a contract settlement on 77,000 workers who were off the job during peak construction season. (Earlier, another 98,000 workers averted a strike with a negotiated settlement.)

The Parti Québécois government wanted to grant the strikers the same contract terms as other workers, meaning a four-year deal with a total of 8.6 per cent in wage increases.

The opposition parties in the minority government balked, and amended the proposed legislation to impose a one-year deal with a two per cent pay hike.

After 14 hours of sometimes bitter debate on Sunday and beyond, Bill 52 was adopted in the early morning hours of Monday as amended.

What all the parties agreed on is that they would prefer a negotiated settlement and the law allows that the imposed settlement will be void if a deal is reached.