In labour law (union law) the arbitrators do not allow these tape recordings into evidence.
In employment law (non unionized law) the case law remains in Ontario that the employee “generally” can secretly tape “relevant” encounters, as long as he/she participates, even slightly, in the discussion.
I put the word generally in quotations, because one has to wonder what would happen if there was a written employment agreement that prohibited that activity.
Also, it must be about “relevant encounters” i.e. if the employee thought he/she was being harassed etc.
The recording might constitute “just cause” for dismissal if it was part of the employee’s general routine or covered sensitive material re other employees etc.
There has been a recent decision out of the British Columbia courts, where the Court of Appeal upheld the trial judge, who found that generalized taping by an employee over time, that had nothing to do with harassment complaints re that employee, and that impinged on the privacy of other employees, was a “revelation of character” and thus constituted “just cause” for dismissal.
Thus, in conclusion, as always, context is key!