The next step could be that they give you a written warning and ask you to sign copy to confirm you have received it. I'm going to guess that there is no staff representation where you work, but ideally, you'd show that letter to someone knowledgeable of such matters who could offer guidance
before you sign it.
I once received such a letter from our HR manager, which I totally ignored, and the subject was
never mentioned again
! I'm not recommending that as a course of action.
B