Relatives of workers surrounding union leader (5)
I believe the answer is:
aunts
'relatives' is the definition.
(aunt is a kind of relative)
'workers surrounding union leader' is the wordplay.
'workers' becomes 'ants' (worker ants).
'surrounding' is an insertion indicator.
'leader' indicates taking the first letters.
The first letter of 'union' is 'u'.
'ants' enclosing 'u' is 'AUNTS'.
'of' is the link.
(Other definitions for aunts that I've seen before include "Female relatives, usually older" , "Relatives get a peculiar US tan" , "Relatives get bad US tan" , "Parents' sisters" , "Elderly female relations" .)