Union Insurance Company v. United States was a case heard by the United States Supreme Court in 1867. The case involved a dispute between the Union Insurance Company and the United States government over the company's right to sue the government for damages. The Union Insurance Company had been hired by the government to provide insurance for a shipment of cotton from New Orleans to New York. The shipment was damaged during the voyage, and the company sought to recover the damages from the government. The Supreme Court held that the Union Insurance Company had the right to sue the government for damages. The Court reasoned that the government had entered into a contract with the company, and that the company had a right to seek damages for any breach of that contract. The Court also held that the government was liable for any damages caused by its negligence or wrongful acts. The decision in this case established the principle that the government is liable for damages caused by its negligence or wrongful acts. This principle has been applied in numerous cases since then, and it remains an important part of the law today.

In the case of Union Insurance Company v. United States, the Supreme Court was asked to decide whether a company could be held liable for taxes on premiums collected from policies issued before Congress passed an act imposing such taxes. The majority opinion found that since the tax had been imposed after the contracts were made, it did not apply retroactively and therefore no liability existed. However, in his dissent Justice Field argued that while there may have been some technical issues with applying this law retroactively, he believed it should still stand as valid legislation because Congress has broad authority to impose taxation when necessary and beneficial for public purposes. He further noted that if companies are allowed to avoid paying their fair share of taxes by simply entering into contracts prior to any new laws being enacted then they would be able to gain an unfair advantage over other businesses who must comply with all applicable regulations.