trade union

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A labor union, especially one limited in membership to people in the same trade.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An organization whose members belong to the same trade and that acts collectively to address common issues.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an organization of employees formed to bargain with the employer