Key U.S. lawmakers urged Japan to strengthen restrictions on sales of chipmaking equipment to China, warning that if Tokyo fails to act, Washington could impose its own curbs on Japanese companies or bar toolmakers that sell to China from receiving U.S. semiconductor subsidies.

The top Republican and Democrat on the House China Select Committee outlined their concerns in a letter dated Oct. 15 to Japanese Ambassador to the U.S. Shigeo Yamada that was reviewed by Bloomberg.

They dismissed arguments that restrictions have had a material negative impact on chip equipment companies like Tokyo Electron, and emphasized the importance of cooperation between the U.S., Japan and the Netherlands — home to the five most important semiconductor toolmakers — in slowing China’s chip ambitions.