Unanimously dismisses union for those seeking shelter (6)
I believe the answer is:
asylum
'shelter' is the definition.
(asylum is a kind of shelter)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for asylum that I've seen before include "A shelter from danger or hardship" , "Madhouse" , "Haven or hospital for the mentally ill" , "Institution for care of the insane" , "Protection given to political refugee" .)