A judge has upheld the TTC's decision to require employees to take random drug and alcohol tests, despite attempts by their union to block the policy.

In a statement, the transit agency said "it felt that it could wait no longer, given the increasing number of positive workplace test results and test refusals it has seen, thereby potentially compromising employee and public safety."

The TTC says random testing will begin later this month after Chief Justice Frank Marrocco, the Associate Chief of the Ontario Superior Court denied the union's application for an injunction.

The Amalgamated Transit Union (ATU) Local 113, which represents TTC employees, also released a statement stating that it will be back in arbitration to overturn "a bad policy that is nothing more than an abuse of employer power against the hardworking women and men who safely move this city."

"While transit workers are disappointed with today's ruling, the judge said himself he's 'satisfied that there are serious issues to be tried at arbitration,'" said Kevin Morton, secretary-treasurer of the union. "Our union is more energized than ever to continue fighting in arbitration against this TTC policy that violates basic human rights."

The decision to implement random alcohol and drug testing was first approved in 2011.

The TTC will randomly test 20 per cent of its more than 10,000 employees annually, including vehicle operators, maintenance workers, supervisors, managers and executives. A third-party provider will generate a random list of workers and conduct the tests on the TTC's behalf.

A breathalyzer will be used to test for alcohol and an oral swab will be used to test for drugs and prohibited substances like marijuana or cocaine. The TTC says the technology will only determine whether or not the employee is impaired at the time of testing.