The TTC has provoked the ire of its largest union by announcing that it will begin randomly testing its employees for drug and alcohol use starting on March 1.

In a news release on Thursday, the transit agency said that it had given formal notice to its workers that it was moving ahead with the plan, which has been in the works for five years.

Under the plan, 20 per cent of employees occupied in “safety sensitive” positions — including some management and executives — would be subject to the tests for drugs and alcohol. Those who would be tested include vehicle operators, maintenance workers, and supervisors.

The release said that the program would only detect “likely impairment” at the time of the test. In response to the news, the union representing 10,000 TTC employees declared it intends to file a court injunction against the testing scheme.

Bob Kinnear, president of Amalgamated Transit Union Local 113, claimed that the Supreme Court has ruled that random drug testing is unlawful unless the employer can show justification.

“It’s clear the TTC does not have the justification for it,” Kinnear said in an interview. “Our members are furious.”

The TTC has said it has legal advice confirming that its plans are legal. Kinnear said that the union planned to file an injunction within a week.

Under a 2010 “fitness for duty” policy, the TTC already tests employees for impairment if management has “reasonable cause” or if the employee is involved in a safety-related incident, has violated the policy, or has returned from addiction treatment.

The agency says that it has seen a sharp increase in positive tests or refusals to be tested in recent years. There were nine in 2011, 16 in 2013, and 27 in 2015.

“This is not acceptable and the TTC cannot wait any longer to act,” the news release said.

Kinnear said he doubted whether the TTC’s numbers could be trusted, but that even if they were taken at face value, they didn’t justify subjecting the bulk of the agency’s workforce to tests that could ruin their livelihood, “because you’ve got half a per cent that may not be able to meet the standard that the TTC is applying.”

A third party would run the testing, the TTC said. Alcohol tests would be done via breathalyzer, while an oral swab would be used for drugs.

It’s not clear how the TTC will pay for the tests. Last week the agency’s board approved $1.3 million in funding for it next year, but that money was not included in a preliminary 2017 budget prepared by city staff this week.

TTC spokesperson Brad Ross signalled that the agency intends to move ahead with the plan regardless.