Can employers ask workers to produce a negative COVID-19 test before returning to work if they had previously tested positive?
Yes, but only as long as you require all workers to get tested before letting them come to work.
Notice, I didn’t use the phrase “return to work.” There’s a reason for that, stemming from the fact that human rights commissions across Canada have made it clear that having or being perceived to have COVID-19 is a disability and thus protected from discrimination.
Consequently, testing a worker who had COVID-19 but not testing another worker who didn’t have COVID-19 is differential treatment that could be considered disability discrimination. On the other hand, testing the worker returning from COVID-19 illness isn’t discriminatory if you test all workers before allowing them to work (or return to work from non-COVID-19-related illnesses or injuries).