In 1890, William McKinley, a Republican member of the United States House of Representatives from Ohio, introduced a tariff bill, which became known as the McKinley Tariff suggesting that protective import taxes should be placed on foreign goods. By this, imported products should become more expensive as compared to similar made in America and by this growing industries within the United States would be protected from foreign competition.
The McKinley Tariff was passed into law in 1890 and dramatically increased the import tax on foreign products. The result was the highest protective import tax in American history to that point, with an average rate of 48 percent. While many business owners supported this legislation many Americans viewed this act as just a method for some businessmen to 'get rich quick' rather than lowering the prices on American goods.
The tariffs of 1890 set the import tax on for example "China, Porcelain, parian" etc. to sixty percent ad valorem and fifty five percent "if not decorated". The tariff law of 1897 - Fifty-fifth Congress, first session - kept the porcelain import tax at this level until further. (Schedule B, #95, page 7).
Regarding the country of origin marking, it was stated in section 6, at page 58 in the original printed Act of 1890:
This specific regulation that was in force from the 1st of March, 1891 did not outlaw the use of Japanese or Chinese or in fact any other characters then the English alphabet from being used or combined with any particular marking, but it definitely for teh protection of the US home market and industry that all imported porcelains should be marked with the country of origin written in the western alphabet. At first, this regulation resulted in that Japanese porcelain were marked "NIPPON" and Chinese "CHINA".
The original name for Japan is a combination of the two characters ni meaning 'day or sun' and hon meaning 'rising' which gave the name 'Nihon', or 'Nippon' that better fitted the Japanese pronunciation. In 1921 the US ruled that 'Nippon' had to be changed into the by then usual Western name 'Japan'.