Workers accept posh relations (5)
I believe the answer is:
aunts
'relations' is the definition.
(aunt is a kind of relation)
'workers accept posh' is the wordplay.
'workers' becomes 'ants' (I've seen this before).
'accept' is an insertion indicator.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'ants' going around 'u' is 'AUNTS'.
(Other definitions for aunts that I've seen before include "Elderly female relations" , "relatively speaking" , "Relatives get a peculiar US tan" , "Relatives get bad US tan" , "Sally and others" .)