Lawyer Blair Pritchett leading marijuana in the workplace seminar in St. John's.

In anticipation of marijuana becoming legal across Newfoundland and Labrador, and in the rest of Canada, employers still have many unanswered questions.

Some of them have been turning to lawyer Blair Pritchett, a partner at McInnes Cooper in St. John's.

He led a half day seminar on Tuesday at Memorial University to brief them about what they'll have to look out for when pot is legalized. 

"I think the biggest issue is going to be …  the issue of residual intoxication," said Pritchett in an interview with CBC Radio's On the Go.

"A lot of drugs … we have a more firm understanding about how long they stay in your system, how long they're psychoactive, and how long they impair your performance, and marijuana that's very much up in the air."

He said it also isn't clear how many people will start smoking weed when it's finally legal.

"There's a small part of me that thinks that this may be another Y2K phenomenon," he said.

"That [day] will come along and the world will keep spinning, and the people that consume marijuana in their own time in their own way will continue to do so and we won't see a serious change in circumstances."

Strict drug testing laws in Canada

One of the things employers will want to do is make sure their employees aren't using or impaired from marijuana while at work. 

Pritchett said in Canada employers can only test employees for intoxication if there's reasonable cause, or if it's suspected following a workplace accident.

"It's certainly not like the United States where you can randomly test your workforce as you see fit," he said.

In the meantime, employers will have to assess on the job performance on a case-by-case basis.

He's hopeful that after legalization there will be more evidence of how long the effects of marijuana linger after ingestion.

"Until there's a bit of an advance in the scientific understanding it's going to be very difficult to sort out when can you comfortably [know] somebody is no longer impaired." said Pritchett.

"But at the end of day, that uncertainty about how many more people will be using, how much bigger a problem might on the job intoxication be, that's what scares people right now."