Union-related state trial fixed (7)
I believe the answer is:
marital
'union-related' is the definition.
(relating to marriage)
'state trial fixed' is the wordplay.
'state' becomes 'ma' (abbreviation for Massachusetts).
'fixed' indicates anagramming the letters.
'trial' anagrammed gives 'rital'.
'ma'+'rital'='MARITAL'
(Other definitions for marital that I've seen before include "Relating to union of husband and wife" , "to do with life together" , "Of a wedding" , "describing matrimony" , "Of nuptials" .)