Stop voting system happening (7)
I believe the answer is:
prevent
'stop' is the definition.
(thesaurus)
'voting system happening' is the wordplay.
'voting system' becomes 'pr' (I've seen this in other clues).
'happening' becomes 'event' (I've seen this before).
'pr'+'event'='PREVENT'
(Other definitions for prevent that I've seen before include "Thwart" , "Avert, hinder" , "Stop (an action)" , "Stop, avert" , "Stop, hinder" .)