Supporting right to advertise (8)
I believe the answer is:
proclaim
'advertise' is the definition.
(I've seen this before)
'supporting right' is the wordplay.
'supporting' becomes 'pro' (I've seen this in other clues).
'right' becomes 'claim' (claim is a kind of right).
'pro'+'claim'='PROCLAIM'
'to' is the link.
(Other definitions for proclaim that I've seen before include "Broadcast" , "advertise" , "Reveal" , "Announce officially or declare publicly" , "Declare formally" .)