The distinctive feature of the NLRB is its two-headed structure: the Board adjudicates, the General Counsel prosecutes, and the two are independent of each other. A case reaches the Board only if the General Counsel has decided to issue a complaint — a decision he takes alone.
This architecture explains much of the instability of American doctrine on joint employment (joint employer). Because it is not fixed by statute or by a lasting regulation, the test has been redefined through successive decisions, in one direction and then the other, as political control has changed hands. The question of whether McDonald's is a joint employer of its franchisees' employees was raised in 2014; it still has no stable answer.