Erie killed general law. Due to statutory, constitutional, and fairness constraints, a federal court generally must apply state substantive law in diversity and supplemental jurisdiction cases.
Since our nation’s founding, however, federal courts have treated equity as an independent branch of general law, binding of its own force in all cases that come before them. In Guaranty Trust Co v York, the Supreme Court held that, notwithstanding Erie, federal courts may continue to rely on traditional principles of equity derived from the English Court of Chancery to determine the availability of equitable relief, such as injunctions, receiverships, and equitable liens, in cases arising under state law. This so-called ‘equitable remedial rights doctrine’ is based on an anachronistic misunderstanding of the nature of the federal equity power. This Article offers a bold new approach to understanding the nature and limits of the federal equity power.
There is no single body of equity law that federal courts must apply in all cases that come before them. In cases arising under state law, there is no basis in the Constitution, federal law, or Federal Rules of Civil Procedure for courts to impose their own equitable standards for relief. Rights and remedies are inextricably intertwined. The manner in which state-created rights are protected is as much a matter of substantive state policy as the state’s initial creation and allocation of those rights. A federal court must apply state statutes and precedents — not uniform, centrally devised federal standards — to determine the availability of equitable relief for state-law claims.
Conversely, for cases arising under federal statutes, the equitable principles that apply are a question of statutory interpretation. When a federal law authorizes equitable relief, a court may presume Congress intended to incorporate traditional equitable principles, absent a clear statement to the contrary in the law’s text or legislative history. And for constitutional cases, federal courts may presumptively apply traditional equitable principles as a matter of constitutional common law, unless Congress chooses to displace it. Thus, contrary to received wisdom, there is no single federal equity law. The scope of equitable relief a federal court may afford depends on the underlying law from which a claim arose.
Morley, Michael T, The Federal Equity Power (March 1, 2017).