Restrains labourers holding strike (9)
I believe the answer is:
handcuffs
'restrains' is the definition.
(restrains using handcuffs)
'labourers holding strike' is the wordplay.
'labourers' becomes 'hands' (hand is a kind of labourer).
'holding' indicates putting letters inside.
'strike' becomes 'cuff' (both can mean to hit).
'hands' enclosing 'cuff' is 'HANDCUFFS'.
(Other definitions for handcuffs that I've seen before include "Restraining devices" , "result in restriction of movement" , "Prisoner restraints" , "Police links" .)