I've always heard "shop" used in relation to a particular business being union or non union in terms of who they hire (i.e. "they're a union shop" means they'll

I've always heard "shop" used in relation to a particular business being union or non union in terms of who they hire (i.e. "they're a union shop" means they'll only hire IATSE or something like that and no non-union people), and "locals" being the actual union you belong to, but that's from the theatre world which might be a bit different.