This was a mistake by many people at Twitter. It is definitely allowed. Whether or not you agree with using someone’s preferred pronouns, not doing so is at most rude and certainly breaks no laws. I should note that I do personally use someone’s preferred pronouns, just as I use someone’s preferred name, simply from the standpoint of good manners. However, for the same reason, I object to rude behavior, ostracism or threats of violence if the wrong pronoun or name is used.