Suncor Energy's attempt to randomly test thousands of its oilsands workers for drugs and alcohol is back under scrutiny as proceedings began again this week.

Arguments are being heard in a labour arbitration in Calgary, with proceedings between Suncor Energy Inc. and the Communications, Energy, and Paperworkers union Local 707 that represents 3,4000 workers, the Globe and Mail reports.

Last November, Alberta's top court dismissed an appeal by Suncor Energy over its plan to randomly test thousands of its oilsands workers for drugs and alcohol.

Justice Jean Cote spoke for the majority at the time, calling Suncor’s plans "a significant breach of worker’s rights," while upholding an injunction that would prohibit the company from testing employees without cause.

New Brunswick's Irving Pulp and Paper is also looking to randomly test employees for alcohol as its mill operations , with the case reaching the Supreme Court of Canada, according to the CBC.

The outcome of these high-profile cases may determine if such testing expands to other workplaces in Canada, CBC adds.

Substance abuse among workers is already a concern in Alberta's oil and gas industry, as workers are exposed to heavy machinery. According to the Globe and Mail, Alberta's courts have been much more likely to allow drug and alcohol testing than in Canada's Eastern and Maritime provinces.

The union argued last year that random testing is an affront to basic human rights, and the Alberta Federation of Labour called the court decision a victory.

“Employers like drug testing programs because they give the impression that something decisive is being done about safety,” Federation president Gil McGowan said in a news release at the time.

“But these programs don’t improve safety. Employers know that, so it’s little more than very expensive public relations.”

Suncor spokeswoman Sneh Seetal said that the oilsands giant was disappointed in the court's ruling.

"We know alcohol and drugs are a pressing safety concern at our Wood Buffalo sites and we will present evidence to support this during the arbitration process."

She said three of the seven workers who died while on the job at Suncor's site since 2000 were under the influence of alcohol or drugs at the time.

"Our view is one fatality is too many."

The union has agreed to certain types of drug testing in its collective agreement, including pre-employment screening and with-cause drug testing, and says there is no evidence that random drug testing makes workplaces safer.

With files from CP

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