The tenth amendment constrains congress from regulating outside enumerated powers. Intrastate trade is not an enumerated power. Most applications of the NLRB are tyrannical short-circuits.
Second: the relevant decision here is NLRB v. Jones & Laughlin, which puts it succinctly[1]:
> Although activities may be intrastate in character when separately considered, if they have such a close and substantial relation to interstate commerce that their control is essential or appropriate to protect that commerce from burdens and obstructions, Congress cannot be denied the power to exercise that control.
I'm not aware of a more recent ruling that changes that doctrine.