A 70-year-old precedent involving an Ohio farmer named Roscoe C. Filburn will be the center of arguments when the health care reform law goes before the Supreme Court March 26. Fillburn sued to overturn a 1938 federal law that told him how much wheat he could grow on his family farm and made him pay a penalty for every extra bushel. The 1942 decision against him is the basis for the Supreme Court’s modern understanding of the scope of federal power. To the Obama administration, the Fillburn decision illustrates how much leeway the federal government has to regulate the choices of individuals affecting the national economy. Opponents of the law say the decision set the outer limit of federal power. The Supreme Court ruling against Filburn was unanimous.