The U.S. Supreme Court case Carnegie-Mellon University et al. v. Cohill, Judge, United States District Court for the Western District of Pennsylvania, et al., 1987 revolved around issues of federal jurisdiction and pendent claims in civil litigation cases. The dispute began when a former employee sued Carnegie Mellon University (CMU) on both federal and state law grounds after being fired allegedly due to his race and union activities. CMU requested that all defendants be tried in federal court under the doctrine of pendent jurisdiction which allows federal courts to hear state-law claims related to their original jurisdiction over a matter based on federal law. However, once all the federally-based claims were dismissed from the lawsuit before trial commenced leaving only state-law claims remaining; Judge Cohill decided not to dismiss these remaining charges but instead chose to retain them within his district court's purview despite objections by CMU who argued this was an abuse of discretion. In its decision, however, the Supreme Court sided with Judge Cohill stating that it is within a district court’s discretion whether or not they wish to keep hearing any supplemental state-law claim(s) even if all originally connected Federal questions have been dropped from consideration priorly.

In the dissenting opinion for Carnegie-Mellon University et al. v. Cohill, Judge, United States District Court for the Western District of Pennsylvania et al., Justice Scalia argued that federal courts should not have discretion to hear state law claims once all federal claims are dismissed before trial. He contended that this contradicts Congress's intent in enacting 28 U.S.C §1367(a), which grants supplemental jurisdiction over state law claims only when they are part of the same case or controversy as a federal claim. According to him, if there is no longer a case or controversy under Article III of the Constitution because all federal-law bases for jurisdiction have been eliminated pretrial, then there can be no supplemental jurisdiction either. This interpretation would promote judicial economy and respect principles of comity by allowing state courts to decide issues involving their own laws without interference from federal courts.