My employer (before LTD) does reasonable cause, post-incident and random testing
for safety-sensitive positions. The substances we test
for are very specific, and are only ones which have the potential to cause impairment (eg: cannabinoids, cocaine, opiates, etc) thus increasing the probability of the employee to cause an incident resulting in injury or death. In Canada, there is no other legally justifiable reason for employers to drug test their employers.