China said it “firmly opposes” a sanctions bill supported by US President Donald Trump that targets countries buying Russian energy.

“China firmly opposes illegal unilateral sanctions that have no basis in international law and are not authorized by the UN Security Council,” Foreign Ministry spokesperson Lin Jian said on Wednesday.

Jian warned “China will take all necessary measures” to protect the interests of its businesses and people. Prioritizing China’s commercial interests indicates the American legislation could significantly affect Chinese firms. The bill would affect third-party entities that facilitate trade with Russia, many of them Chinese.

The bill has not yet passed, as it was just proposed in the US Senate. But it will likely be approved, as it has bipartisan support. Senate Minority Leader Chuck Schumer, of the Democrats, has also spoken favorably about the bill, urging senators to pass it in order to “support Ukraine.”

If passed, it will likely upset the Chinese, who may consider retaliatory measures, including tightening export controls on critical materials. China is the world’s dominant producer, processor, and holder of rare earth mineral reserves, which are essential for modern technology, national defense, and green energy infrastructure.

This is not the first time China has spoken against Western sanctions on suppliers to Russia. In May, the UK government sanctioned entities for supplying military components, two of which were Chinese. Jian criticized the move at the time, saying China had “lodged serious protests” with the British. He argued that China supports a diplomatic solution to the war and that “normal exchanges and cooperation between China and Russia should not be disrupted or affected.”