Employ union - it lies to order (7)
I believe the answer is:
utilise
'employ' is the definition.
(I know that employ can be written as utilise)
'union it lies to order' is the wordplay.
'union' becomes 'U' (common abbreviation as in 'Trades Union Congress').
'to order' indicates an anagram.
'it'+'lies'='itlies'
'itlies' anagrammed gives 'tilise'.
'u'+'tilise'='UTILISE'
(Other definitions for utilise that I've seen before include "Employ, do something with" , "Put to use" , "Find application or task for" , "Employ, make use of" , "Put into service, find application for" .)