He breaks more than one union law (8)
I believe the answer is:
bigamist
'he breaks more than one union law' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is all the clue.
Can you help me to learn more?
(Other definitions for bigamist that I've seen before include "Marital cheat" , "Law-breaker with more than one spouse" , "One who marries more than once illegally" , "One with a partner too many" , "One marrying too often" .)