It may seem odd that an employer can discriminate against an employee based on a mental or physical disability when the employee doesn’t actually have a disability. It is, however, a legal concept which seems to make good sense in practice.
In effect, an employer who deals with an employee as if he or she suffers from a disability is treated, for the purposes of human rights law, as it would be if the employee does have a disability. Though it may be difficult to imagine why an employer would do that, this isn’t a particularly rare occurrence.
This concept has perhaps arisen most frequently in relation to mandatory drug testing imposed on employees. Such drug testing policies effectively treat employees as if they are drug dependent (which is a disability) and are likely to attend at work in an impaired state.
The great majority of employees are, of course, not addicted to drugs. However, by imposition of a mandatory drug testing policy, the employer presumes or perceives them to be addicted.