Block vote? (4)
I believe the answer is:
veto
This clue is a double definition.
'block' is the first definition.
(to veto is to block a decision or action)
'vote?' is the second definition.
(I know that veto is a type of vote)
(Other definitions for veto that I've seen before include "Ban; refuse to allow" , "Formally forbid" , "Refuse permission" , "black ball" , "Refuse to endorse" .)