It means asking for the nullity of any decision, for reasons of illegality, injustice or fraud, also because you have not had due process or not to have followed the necessary and required procedures. It means rejecting the validity of an assertion, idea or argument by reason or proof. Rebut, disprove, contradict, censor.
* Only one "like" per meaning and day, the more "likes" the meaning will appear higher in the list