“ The Board will assert jurisdiction over an employer operating a radio station if his gross receipts equal or exceed $100,000 per year, Raritan Valley Broadcasting Co. 122 N.L.R.B. 90, and in determining the relevant employer, the Board considers several nominally separate business entities to be a single employer where they comprise an integrated enterprise, N.L.R.B Twenty-first Ann.Rep. 14-15 (1956) . The controlling criteria, set out and elaborated in Board decisions, are interrelation of operations, common management, centralized control of labor relations and common ownership. ”

“ Sakrete of Northern California, Inc., 137 N.L.R.B. 1220, aff'd 332 F.2d 902 (C.A.9th Cir.) , cert. denied, 379 U.S. 961, 85 S.Ct. 649, 13 L.Ed.2d 556; Family Laundry, Inc., 121 N.L.R.B. 1619; Canton, Carp's, Inc., 125 N.L.R.B. 483; V.I.P. Radio, Inc., 128 N.L.R.B. 113; Perfect T.V., Inc., 134 N.L.R.B. 575 ”