This week, I taught cases on enumerated powers from the Progressive Era and during the New Deal. In Hammer v. Dagenhart (1918), the Supreme Court declared unconstitutional a federal law that banned the transportation of good made by child labor. The Court found that this law was in fact an attempt to regulate local labor conditions, and the focus on shipping the goods was something of a pretext.
More than two decades later, the Supreme Court overruled Hammer in United States v. Darby (1941). This precedent upheld the constitutionality of the Fair Labor Standards Act (FLSA). Darby was largely an extension of NLRB v. Jones & Laughlin Steel (1935). These two decisions replaced the "direct effects" test with the "substantial effects" test. Under this regime, Congress could regulate any local activity that had a substantial effect on interstate commerce. The Court would also review such regulations with something akin to rational basis scrutiny, and require only a reasonable fit between the means Congress has taken, and the ends Congress is seeking to accomplish.
While teaching Darby, I wondered how Solicitor General Francis Biddle distinguished Hammer. So I pulled the government's brief. To Biddle's credit, he acknowledged that the FLSA contained a child labor provision that was "identical" to the law declared unconstitutional in Hammer:
