Start playing up after industrial action (6,2)
I believe the answer is:
strike up
'start playing' is the definition.
(synonyms)
'up after industrial action' is the wordplay.
'after' says to put letters next to each other.
'industrial action' becomes 'strike' (workers going on strike).
'up' put after 'strike' is 'STRIKE-UP'.
(Other definitions for strike up that I've seen before include "Start playing music - begin (acquaintance) - emboss" , "Begin to play (a piece of music)" .)