Fear led to shift supporting Union (7)
I believe the answer is:
federal
'supporting union' is the definition.
'federal' can be an answer for 'union' (I've seen this before). I am not sure about the 'supporting' bit.
'fear led to shift' is the wordplay.
'to shift' indicates anagramming the letters.
'fear'+'led'='fearled'
'fearled' anagrammed gives 'FEDERAL'.
Can you help me to learn more?
(Other definitions for federal that I've seen before include "(Of institutions) combined" , "Red leaf (anag.)" , "(Of a union or government) involving states voluntarily joined together for common purposes" , "Relating to a treaty" , "National, in the US" .)