Ain't gonna work on Saturday

Badatz has started giving hechshers to... real estate companies. First up: an Israeli firm with a branch in Canada.

As far as Shabbat is concerned, Rabbi Klein clarified that the Badatz review found that there are Jewish employees in the Canadian office who do not take off Saturdays. Badatz, therefore, made its granting of the kashrut certificate conditional on the Jewish employees stopping to work on Saturdays and permitted non-Jewish employees to continue working.

I'd like to know how this works in Canadian law. Is it religious discrimination to tell a Jewish employee they are no longer allowed to take a Saturday shift, or come in on a Saturday if they want to, while other employees can?