A New Jersey food importer filed a lawsuit Tuesday challenging Donald Trump’s power to invoke a Depression-era law to levy a 50% tariff on $20 billion worth of Canadian goods.

The Gellert Global Group, a third-generation family business that imports Canadian cheese, took its case to the U.S. Court of International Trade, a specialized court in New York.

In August, Trump reached back to Section 338 of the Tariff Act of 1930 to impose the tariffs on Canada, prompting dollar-for-dollar retaliation from Ottawa and straining already-tense relations between the neighbors and longtime allies. The president last month escalated the conflict by announcing an outright ban on nearly $1 billion worth of Canadian products, including alcoholic beverages, dairy products and motorcycles.