W.W. Grainger, Inc. v. N.L.R.B

In W.W. Grainger, Inc. v. NLRB, 860 F.2d 244, 247 (6th Cir. 1988), the court stated that the factual question of whether two employers are joint depends on factors such as "the supervision of the employees' day-to-day activities, authority to hire or fire employees, promulgation of work rules and conditions of employment, work assignments, and issuance of operating instructions."