Ban; refuse to allow (4)
I believe the answer is:
veto
I believe this is a double definition.
'ban' is the first definition.
(veto can mean a ban or prohibition on something)
'refuse to allow' is the second definition.
(I've seen this before)
(Other definitions for veto that I've seen before include "Vote to block a decision" , "Right to prevent proposed action" , "The power to prohibit or reject a proposal" , "Literally, 'I forbid'" , "Overrule, forbid" .)