Strike is a barrier to work (6)
I believe the answer is:
wallop
'strike' is the definition.
(I've seen this before)
'barrier to work' is the wordplay.
'barrier' becomes 'wall' (a wall acts as a barrier).
'to work' becomes 'op' (abbreviation for opus).
'wall'+'op'='WALLOP'
'is a' is the link.
(Other definitions for wallop that I've seen before include "Beer - hit hard" , "big hit" , "Punch" , "A heavy resounding blow (6)" , "batter" .)