The US has announced new rules targeting firms from China and other countries that are routing shipments of steel and aluminium through Mexico to try to evade tariffs.
The White House said firms shipping via Mexico must now prove the origins of their products if they want to avoid the border taxes.
The move comes as President Joe Biden seeks to prove his tough-on-China credentials as he faces off against his predecessor, Donald Trump, in the 2024 presidential election.
The measures expand protections for US steel and aluminium-makers that were launched under Mr Trump in 2018 in the name of national security.
The tariffs, which set a 25 percent tax on steel and a 10 per cent tax on aluminium imports, were controversial, sparking trade battles with countries around the world.
Mexico, one of America's largest trade partners, was among the countries to eventually win an exemption from the rules.