[A]cts which directly burden or obstruct interstate or foreign commerce, or its free flow, are within the reach of the congressional power.
NLRB v. Jones & Laughlin Steel Corp
Congress passed the National Labor Relations Act, which prohibited discharging employees for union activities and other "unfair labor practices affecting [interstate] commerce." A Pennsylvania corporation ran afoul of this law.
Does Congress have the power to regulate labor practices that "affect interstate commerce"?
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The act says it only applies to unfair labor practices "affecting commerce," and commerce which is defined in the constitutional sense. It purports to only affect what could obstruct such commerce, which is allowed within the Constitution. As its effect is what matters and not its source, it does not matter that this law deals with labor disputes. While defendant's manufacturing itself may not be commerce, Congress has power over any danger that threatens commerce. An industrial war would have consequences on interstate commerce, so Congress must have power over it.
Yes, Congress can regulate anything that interferes with interstate commerce.
Any effect on interstate commerce here would be indirect and very remote. The discontent would have to cause a strike, which would have to result in reducing production, which would have to reduce the volume of goods being sold out of state, which the legislation finally purports to concern itself with. If something this remote affects commerce enough to justify regulation, then almost anything in life could be said to. Yet Congress' power only extends to direct and material interference with commerce, not some mere possibility contingent on such uncertain events.