company union vs labor union

company union and labor union both are nouns.

Word	Noun	Adjective	Verb	Adverb
company union	Yes	No	No	No
labor union	Yes	No	No	No

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

company union: a union of workers for a single company; a union not affiliated with a larger union
labor union: an organization of employees formed to bargain with the employer

Other hypernyms of company union include brotherhood, trade union, trades union, union.

company union (noun)	labor union (noun)
a union of workers for a single company; a union not affiliated with a larger union	an organization of employees formed to bargain with the employer