Board Thread:Support Requests - Community Management/@comment-35434621-20151108202544/@comment-3026053-20151108203427

There is no set rule about this, as it generally varies depending on the matter in which the rules were broken. For example, you can have users that come to your wiki and start blanking pages left and right. Those are clear vandal accounts and can generally be blocked on sight -though there is nothing wrong with issuing a warning first. On the other hand, you can also have users who do things that are against your wiki's rules, but could easily be covered with "good faith, they didn't mean to do it". In such cases, at least one warning before further action should be issued. In general, it's always best to try to give people the benefit of the doubt and try to educate them in the way of your wiki as opposed to immediately strike them down.

So the short answer to your question: do what you feel is appropriate in regards to the edits made by the user who broke the policy and your own sense of justice and how you'd like to be treated if you were in their shoes.