The proclamation, based on Section 232 of the Trade Expansion Act of 1962, followed a yearlong national security investigation by the Commerce Department into polysilicon production. The tariff on polysilicon derivatives takes effect after 120 days. Commerce Secretary Howard Lutnick said the price floors were designed to prevent Chinese producers from selling below cost in the U.S. market. The move is not the first time Washington has targeted Chinese polysilicon. That the administration paired a relatively modest 15% tariff rate with an extensive minimum price system, rather than relying on a higher tariff by itself, suggests officials concluded that price floors offer more durable protection against Chinese underpricing than tariff rates alone, which exporters can sometimes absorb or offset through further price cuts.