In the case of Linn v. United Plant Guard Workers of America, Local 114, et al., the Supreme Court ruled that federal courts have jurisdiction over cases involving libelous statements made during labor disputes under Section 301(a) of the Labor Management Relations Act (LMRA). The plaintiff, Robert Linn, was a manager at Pinkerton's Inc., who claimed he had been defamed by false accusations from union members stating he committed acts of violence against them. The court held that while unions and their members are allowed some leeway in making derogatory remarks about management during labor disputes due to "the heat of such controversies," they can be held liable for maliciously spreading damaging falsehoods. However, it also established a higher standard for proving malice in these situations than is typically required in other defamation suits - plaintiffs must show not only that the statement was untrue but also that it was made with knowledge or reckless disregard as to its falsity.

In the dissenting opinion for Linn v. United Plant Guard Workers of America, Local 114, Justice Black argued that federal courts should not have jurisdiction over libel cases arising from labor disputes because such matters are more appropriately handled by state courts. He believed that Congress intended to leave regulation of defamatory statements in labor disputes largely to the states when it passed the National Labor Relations Act (NLRA). Furthermore, he contended that extending federal jurisdiction could potentially infringe upon First Amendment rights as it might discourage robust debate and free expression within labor unions. In his view, this case did not present a significant threat to industrial peace warranting federal intervention; rather it was essentially a personal dispute between individuals which had little impact on broader labor relations or interstate commerce. Therefore, he disagreed with majority's decision allowing plaintiff to pursue damages under federal law for malicious libel during a union organizing campaign.