What are your qualifications?

This is the fallacy that if someone has not studied or been educated in a particular topic on a high enough level, then that person is not allowed to criticize that topic of interest at all. It is an argument from authority, except in reverse.

It is deemed a fallacy for the reason that information is legitimate or illegitimate without needing the person stating it to be an expert or even authoritative. If someone is an expert then they may know more on the subject, may be more likely to be correct or be more believable, but that doesn't discredit the information.