Construction companies, building owners, and unions are worried about what legalizing marijuana will mean for their industry.

Representatives from several construction-related groups discussed the issue Monday at meetings taking place in Montreal.

Monia Vallée of the Provincial association of housing construction in Quebec (APCHQ) said she expects cannabis consumption will increase once the drug is legalized, and pointed out there are already frequent complaints.

"Currently we have cases we're aware of where cannabis is being consumed in workplaces, on construction sites. There are workers who use during a meal period or on a break. It's already a problem on construction sites," Vallée told the Canadian Press.

"Whether cannabis is legal or not, it's zero tolerance on all construction worksites and we will maintain and hammer on that message."

Union leaders are also unimpressed with the federal government's plan to legalize cannabis, with FTQ Construction head Yves Ouellet calling it amateurish.

Others are worried that youth don't believe there are any harmful effects of cannabis and as a result may think it's acceptable to come to work while high.

The APCHQ is going to publish guidelines about drug and alcohol use on its website.

With a file from The Canadian Press