there is in fact a proper precedent in canadian law - well tested - about the restriction of political activities by public employees.

so, for example, if you work for the government, you can't organize a protest against it. is that a restriction of expression? absolutely, perhaps. but, it is upheld by the need to ensure for neutrality in government - you can't have activists running public services.

this law is actually more lenient than the precedent would allow for, as the precedent bans all political expression, not just inside work but outside of it as well.