The U.S. government is making it harder for the South Korean chipmakers Samsung and SK Hynix to secure American equipment for their factories in China, hamstringing their operations in the country and walling Beijing off from certain semiconductor technology.

The Commerce Department said on Friday that it would revoke authorizations that had allowed the companies to ship critical semiconductor machinery to China. The companies will now need to secure licenses from the Trump administration if they want to purchase American equipment for their Chinese factories.

Under former President Joseph R. Biden Jr., the U.S. government issued sweeping restrictions in 2022 in an attempt to cut off China’s access to important American technology. But in 2023 it granted waivers to the South Korean chipmakers.

The current administration’s move takes aim at two of South Korea’s most important companies. It could also put a strain on trade discussions between South Korea and the United States just as many of Mr. Trump’s tariffs were invalidated by a federal court. President Trump and South Korea’s president, Lee Jae Myung, met earlier this week to discuss how to make progress in continuing trade negotiations, which have yet to be codified in any public documents.

Samsung declined to comment. Yixi Lee, a spokesperson for SK Hynix, said in a statement that the company would “maintain close communication with both Korean and the U.S. governments and take necessary measures to minimize the impact on our business.”

Chipmakers have been on the front lines of an escalating face-off between the United States and China, the world’s two biggest superpowers, that has increasingly involved advanced technology. Washington is trying to cut off China’s access to semiconductors to stunt Beijing’s progress in developing artificial intelligence.