Strikebreakers using small taxis (5)
I believe the answer is:
scabs
'strikebreakers' is the definition.
('scab' can be a synonym of 'strikebreaker')
'small taxis' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'taxis' becomes 'cabs' ('cab' can be a synonym of 'taxi').
's'+'cabs'='SCABS'
'using' is the link.
(Other definitions for scabs that I've seen before include "Wound crusts" , "Blacklegs, strikebreakers" , "They continue to work" .)