In the case of United States et al. v. Saskatchewan Minerals, 1966, the U.S Supreme Court was tasked with determining whether a Canadian corporation could be held liable for antitrust violations under American law. The Canadian company, Saskatchewan Minerals, had been selling potash in the US and allegedly conspired to fix prices with other companies which is illegal under US antitrust laws. However, they argued that as a foreign entity not based or incorporated in America they were exempt from these regulations. The court ruled against Saskatchewan Minerals stating that any business operating within U.S borders must adhere to its laws regardless of where it's headquartered or incorporated. This decision set an important precedent for future cases involving international corporations doing business in America by confirming that such entities are subject to U.S anti-trust legislation when conducting operations within its jurisdiction.

In the dissenting opinion for the United States v. Saskatchewan Minerals case, it was argued that the majority's decision to uphold a tariff on imported potash was incorrect. The dissenting justices believed that this ruling contradicted previous court decisions and violated international trade agreements. They contended that potash should be classified as a mineral, not a chemical compound, which would exempt it from certain tariffs under existing laws and treaties. Furthermore, they disagreed with the majority's interpretation of legislative intent behind these laws and treaties - arguing instead that Congress intended to promote free trade rather than protect domestic industries through protectionist measures like tariffs. Therefore, in their view, imposing such tariff on imported potash unfairly disadvantaged foreign producers while benefiting American ones at odds with both legal precedent and policy objectives.