Aim of protest (6)
I believe the answer is:
object
I believe this clue is a double definition.
'aim' is the first definition.
(I know that aim can be written as object)
'protest' is the second definition.
(as in objecting to something)
'of' is the link.
(Other definitions for object that I've seen before include "design?" , "Thing; complain" , "Sporting description of ball" , "end" , "Thing or target" .)