Tariffs– fees charged by the U S Government for the import of goods– are designed to protect politically-powerful interests who would otherwise be unable to compete as profitably with foreign producers. So they are regressive in the sense that politically-powerful interests are likely to be relatively wealthy.
But according to this article, tariffs are also regressive in the sense that their direct impact on the poor exceeds that on the wealthy. “Luxury goods have very low tariffs, while cheap clothes, underwear, shoes and household products have much higher rates.” Several examples are cited; I have no idea whether they’re typical. Both the Cato Institute and the Democratic Leadership Council are quoted in support, an official of the former calling tariffs “our most regressive tax that the federal government imposes.”