US trade officials fear their Chinese counterparts could be using a back door into the American market, trying to avoid paying taxes by sending metals through Mexico. They announced on Wednesday that they are imposing tariffs on foreign-made steel and aluminum shipped from Mexico.

The US officials allow imports from Mexico duty-free as part of the North American trade agreement. They have seen officials in China take advantage by shipping their products through Mexico. They will impose a 25 percent tariff on steel imports that are melted and poured outside Mexico, the US or Canada. They will impose a 10 percent tariff on imports of aluminum, hitting production based in China, Russia, Belarus and Iran.

Mexican officials have joined the effort. They have agreed to require importers of steel products to provide information on the country of origin.

White House officials said President Joe Biden is taking action to close a "loophole" left open by his predecessor, Donald Trump. They said the gap has allowed cheap Chinese metals, supported by government subsidies, to flood the US market. Biden is hoping to protect domestic manufacturers and workers as he runs for reelection.