In N.L.R.B. v. Nu-Car Carriers, Inc., 189 F.2d 756 (3rd Cir. 1951), cert. den., 342 U.S. 919, 72 S.Ct. 367, 96 L.Ed. 687 (1952), workers who leased tractors from a corporation were held to be employees, on the grounds that express contractual provisions placing the workers under the direction and supervision of the corporation were enforced by supervisors who checked up on the quality of their driving, discharged, and at times assigned routes to the workers.