TORONTO -- Regional transit agency Metrolinx plans to ban workers in so-called safety sensitive positions from using recreational cannabis on or off duty.

The provincial agency that operates in the Greater Toronto and Hamilton Area says workers in approximately 140 roles-- including vehicle operators -- will be banned from using pot under the policy that take effect Feb. 1.

It says it is making the change to fitness-for-duty rules to ensure the health and safety of its employees, the public, and the communities it serves.

The union representing some of the agency's workers says it is exploring a possible court challenge of the policy.

The Amalgamated Transit Union says the rules overreach into worker's private lives and violate their constitutional rights.

Recreational marijuana has been legal in Canada since October 2018.