a closed shop

a closed ˈshop

a factory, etc. where only people belonging to a certain union may work
See also: closed, shop
References in periodicals archive ?
The latter not only insist on Premiership clubs being the only ones to run recognised youth academies,but operate such a closed shop that Rotherham, who were refused promotion to the Premiership 12 months ago,have only been grudgingly admitted the second time round,and even now will not receive as much cash as their club rivals.