closed shop

closed shop  {n. phr.}

1. A plant or factory that employs only union workers.

Our firm has been fighting the closed shop policy for many years now.

2. A profession or line of work dominated by followers of a certain mode of thinking and behaving that does not tolerate differing views or ideas.

Certain groups of psychologists, historians, and linguists often behave with a closed-shop mentality.

Contrast: OPEN SHOP.