Workers' associations in unison perhaps (6)
I believe the answer is:
unions
'workers' associations' is the definition.
(I've seen this before)
'unison perhaps' is the wordplay.
'perhaps' indicates an anagram.
'unison' with letters rearranged gives 'UNIONS'.
'in' acts as a link.
(Other definitions for unions that I've seen before include "Undoes a knot" , "Acts of joining together" , "Trade organisations" , "Marriages or workers' organisations" , "Couplings and labour organisations" .)