Industrial action is a hit! (6)
I believe the answer is:
strike
I believe this clue is a double definition.
'industrial action' is the first definition.
(workers going on strike)
'a hit' is the second definition.
(I know that hit can be written as strike)
'is' is the link.
(Other definitions for strike that I've seen before include "Hit; withdraw labour" , "Industrial dispute - everybody out" , "Hit or take industrial action" , "Agree on" , "Hit the labour withdrawal" .)