"No, it is a matter of principle!"
Translation:Non, c'est une question de principe !
I've never heard such a thing, "question de principe" is for me the only right answer.
Thanks. I note that Collins Dictionary translates "a matter of" to "une question de". See: https://www.collinsdictionary.com/dictionary/english-french/matter
I don't think so. Just for starters, there's
Very few results returned for "il s'agit de principe" (in quotes).
The question is not what is used more often. That is never the question. It is whether the OP's translation is correct or not. Otherwise, only one answer would ever be acceptable.
I was marked wrong for "c'est une chose de principe", which I think should work. I've reported it, but I'm not sure it's acceptable.