(formerly) an establishment whose employment policy is governed by a contract between employer and a trade union permitting the employment of nonunion labour only on the condition that such labour joins the union within a specified time period
Compare open shop, closed shop
union shop in American English
US
1.
a factory, business, etc. operating under a contract between the employer and a labor union, which permits the hiring of nonunion workers but requires that all new employees join the union within a specified period