In Rondeau v. Mosinee Paper Corp., the Supreme Court ruled that a federal court could not issue an injunction requiring a party to comply with Section 13(d) of the Williams Act, which mandates disclosure when acquiring more than five percent of a company's stock. The case involved James E. Rondeau, who had acquired over ten percent of Mosinee Paper Corporation’s shares without disclosing his holdings as required by law. When this was discovered, Mosinee sued for injunctive relief and damages under Section 18(a) of the Securities Exchange Act and Rule 10b-5 thereunder, alleging fraud in connection with purchase or sale of securities due to nondisclosure. The Supreme Court held that while it is true that Rondeau violated section 13(d), he did so only once and promptly corrected his mistake upon discovery; therefore no irreparable harm was done to warrant an injunction against him from further violations. Furthermore, they found no evidence supporting allegations made under Rule 10b-5 about fraudulent practices affecting public investors or causing injury to corporate assets or business reputation.

The dissenting opinion in the case of Rondeau v. Mosinee Paper Corp., argued that the majority's decision was too narrow and failed to fully consider the broader implications of securities law violations. The dissent believed that a violation of Section 13(d) should be considered irreparable harm, warranting injunctive relief, even if there is no immediate threat to corporate control or policy changes. They contended that this section was designed not only to prevent secret takeovers but also to provide shareholders with information necessary for informed voting decisions. Therefore, any violation undermines shareholder democracy and constitutes an ongoing injury until corrected by full disclosure. Furthermore, they disagreed with the majority's view on balancing hardships between parties before granting injunctions in these cases; arguing it could potentially allow violators benefit from their wrongdoing while victims suffer without remedy.