Begin to play as industrial action increases (6,2)
I believe the answer is:
strike up
'begin to play' is the definition.
(as in beginning a piece of music)
'industrial action increases' is the wordplay.
'industrial action' becomes 'strike' (workers going on strike).
'increases' becomes 'up' (I can't justify this - if you can you should give a lot more credence to this answer).
'strike'+'up'='STRIKE-UP'
'as' is the link.
Can you help me to learn more?
(Other definitions for strike up that I've seen before include "Begin to play (a piece of music)" , "Start playing music - begin (acquaintance) - emboss" .)