Industrial action is blow (6)
I believe the answer is:
strike
I believe this is a double definition.
'industrial action' is the first definition.
(I've seen this before)
'blow' is the second definition.
(strike is a kind of blow)
'is' acts as a link.
(Other definitions for strike that I've seen before include "Hit with picket?" , "Sudden attack; chime" , "Hit; withdraw labour" , "Agree on" , "coin" .)