I object to a certain action (7)
I believe the answer is:
measure
'action' is the definition.
(measure is a kind of action)
'i object to a certain' is the wordplay.
'i object' becomes 'me'.
'certain' becomes 'sure' (synonyms).
'me'+'a'+'sure'='MEASURE'
(Other definitions for measure that I've seen before include "Portion" , "of specified size" , "Determine the size of" , "See 1" , "bar of music" .)