MONTREAL -- Quebec's striking crane operators defied an order to return to work on Friday, as the province's transport minister announced the government's intention make the union pay the costs of the strike.

Andre Fortin said in a statement that he was preparing to send a formal notice to the crane operators' union in order to claim damages for what he described as an illegal strike.

"For almost a week, crane operators have been carrying out an illegal strike and that is unacceptable," he said.

"Worksite delays represent significant costs that taxpayers shouldn't have to pay."

In a press conference, Quebec's premier reiterated the message that striking workers would face consequences.

"(To) those who think that because there are elections coming up, the government would haggle some kind of solution outside of the law, remove this illusion from your mind," Philippe Couillard told reporters.

Quebec's construction commission said most of the crane operators stayed off the job for a fifth straight day on Friday despite a labour board ruling ordering them back to work.

In granting the interim order on Thursday, the tribunal ruled that the urgency to act was justified because the strike was having a significant impact on worksites.

The tribunal will decide at a later date whether the actions constituted a illegal strike when it hears the case on its merits.

The operators are protesting changes made to training requirements that will allow workers to operate cranes without first obtaining a vocational diploma.

Crane operators say the new training program is less comprehensive and could lead to a rise in workplace accidents.

The construction commission, which enforces industry labour rules in Quebec, had argued the strike is illegal because crane operators are under contract until 2021.

The collective agreement prohibits ordering, encouraging or supporting a strike, slowdown or lockout.

There are 1,856 crane operators in the province and 1,573 of them are represented by two major unions whose lawyers argued against the order on Thursday.