President Donald Trump adjusted his national security tariffs on steel, aluminum and copper imports on Thursday to cut duty rates on derivative products made with the metals, simplify compliance and avoid under-reporting of import values.

In a proclamation signed by Trump, the United States will maintain a 50% import tariff on steel, aluminum and copper commodity imports under Section 232 of the Trade Act of 1974, but apply the rate to the prices paid by U.S. customers, according to a White House announcement and a senior Trump administration official.

It was not immediately clear how the sales price and resulting tariff would be determined.

The official said some importers had been claiming artificially reduced import values to reduce their tariff costs.