Having a bias is a form of corruption for a referee.
I'm being totally serious when I say this: if I was a professional ref and was asked to referee a Man Utd game, I would refuse. There's not a chance I could referee that game fairly.
Tierney, England, Kavanaugh and Oliver are objectively anti-Arsenal. Their performances have shown they cannot be neutral in an Arsenal match. Even if its existence is not made public, a competent body should analyse refereeing performances for irregularities such as bias.
This isn't only for the benefit of Arsenal. There'll be refs that are biased against Liverpool or Newcastle or Villa. Man City are unscathed because they may be paying off refs and they're a small club so no-one outside of north London and Liverpool feels strongly about them.