Marjaleena, an example of different circumstances are in my last comment:
a. international air travel - probably essential to see the face
b. local streetcar travel paid by cash - no reason to see the face.

Three levels of court did a 'balancing' exercise in the case of R. v. N.S. - a sexual assault complainant who wanted to wear her niqab while giving evidence.  In the end, she was not allowed to, but the Supreme Court said that witnesses may wear a niqab for religious purposes while giving evidence where credibility is not in issue.

You can read the factors the Supreme Court considered in coming to that conclusion, here:
https://scc-csc.lexum.com/scc-csc/scc-csc/en/item/12779/index.do?r=AAAAAQAFbmlxYWIB