President Donald Trump said Tuesday he’s imposing a new 50% tariff on all copper imported into the US. However, it’s unclear when the new tariff would take effect. “Today we’re doing copper,” he said at a Cabinet meeting,

The Yale Budget Lab noted that the letters sent Monday would hike the effective tariff rate on U.S. consumers to the highest since 1934.

Trump sent letters to 14 countries threatening them with new tariffs, and the White House said more countries may be included in the coming days.