Voting system is possible as form of punishment! (6)
I believe the answer is:
prison
'form of punishment' is the definition.
'voting system is possible' is the wordplay.
'voting system' becomes 'pr' (I've seen this in other clues).
'possible' becomes 'on' ('not on' can mean unacceptable or not possible).
'pr'+'is'+'on'='PRISON'
'as' is the link.
(Other definitions for prison that I've seen before include "cage" , "Stir - can" , "Slammer" , "Place of detention for criminals" , "Place of incarceration" .)