union member vs worker

union member and worker both are nouns.

Word	Noun	Adjective	Verb	Adverb
union member	Yes	No	No	No
worker	Yes	No	No	No

As nouns, worker is a hypernym of union member; that is, worker is a word with a broader meaning than union member:

union member (noun)	worker (noun)
a worker who belongs to a trade union	sterile member of a colony of social insects that forages for food and cares for the larvae
	a person who works at a specific occupation
	a member of the working class (not necessarily employed)
	a person who acts and gets things done