Western Air Line Construction Company v. McGillis was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue an injunction against a federal court. The case arose when the Western Air Line Construction Company (WALC) sought to enjoin the McGillis family from interfering with its construction of a railroad line in the state of California. The McGillis family had obtained an injunction from the state court, which WALC argued was in violation of the Supremacy Clause of the United States Constitution. The Supreme Court held that the state court did not have the authority to issue an injunction against a federal court. The Court reasoned that the Supremacy Clause of the Constitution gave the federal courts exclusive jurisdiction over matters involving the federal government. The Court further held that the state court's injunction was in violation of the Supremacy Clause and was therefore invalid. In conclusion, the Supreme Court held that the state court did not have the authority to issue an injunction against a federal court. The Court reasoned that the Supremacy Clause of the Constitution gave the federal courts exclusive jurisdiction over matters involving the federal government. The Court further held that the state court's injunction was in violation of the Supremacy Clause and was therefore invalid.

In Western Air Line Construction Company v. McGillis, the Supreme Court was asked to decide whether a contract between two parties could be enforced when one of them had died before it was fully performed. The majority opinion held that the contract could not be enforced because it had been made with an individual and thus did not survive his death. In dissent, Justice Field argued that contracts should generally be enforceable even if one party has died since they were entered into as long as there is no evidence to suggest otherwise in the language of the agreement itself or in other applicable laws. He further noted that this rule would promote fairness and justice by ensuring both parties are held accountable for their obligations under any given agreement regardless of changes in circumstances beyond their control such as death or illness.