(Bloomberg) — Samsung Electronics Co. (005930.KS, SSNLF) and SK Hynix Inc. (000660.KS, HXSCL) shares slid Monday after the Trump administration decided to make it harder for the world’s largest memory chipmakers to ship critical equipment to their giant Chinese operations.

The surprise ruling deals a potential blow to their production in the world’s largest semiconductor market. While both Korean companies have memory plants in Korea, China accounts for a major slice of their global output. Samsung sank more than 2%, while SK Hynix stock was more than 4% lower in morning trading.

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Samsung and Hynix compete with Micron Technology Inc (MU). to make key components for most electronics from Apple Inc (AAPL). iPhones to Nvidia Corp. (NVDA) AI servers. The pair had operated in China under regulations that allow them to import chipmaking equipment without applying for a new license each time. They now have 120 days until the waiver expires, according to an announcement in the US Federal Register. Companies can seek licenses to continue operations.

The Trump administration’s move would revise what’s known as the validated end user, or VEU, rules, handicapping the ability to make chips in the country and jeopardizing Beijing’s access to certain technologies.

On Monday, shares in the Korean firms’ suppliers also weakened. Advantest Corp., (ATEYY) which gets an estimated 10th of its revenue from Samsung, slid more than 7%. Disco Corp. (DSCSY) stock also fell more than 7%, while leading supplier Tokyo Electron Ltd. (TOELF) declined more than 2%.

Those waivers date back to 2023 when then-President Joe Biden’s administration moved to allow the South Korean chipmakers to acquire the equipment they need to sustain and expand their giant operations in China. Washington effectively granted an indefinite waiver on broader restrictions banning the shipment of advanced chipmaking gear to the country.

SK Hynix said in a statement Friday it would “maintain close communication with both Korean and the US governments and take necessary measures to minimize the impact on our business.” Samsung didn’t respond to a request for comment.

“The Trump administration is committed to closing export control loopholes — particularly those that put US companies at a competitive disadvantage,” Under Secretary of Commerce Jeffrey Kessler, who oversees export control programs, said in the statement. “Today’s decision is an important step towards fulfilling this commitment.”

The US decision emerged days after President Donald Trump met his South Korean counterpart, President Lee Jae Myung, at the White House. In their meeting, the two men discussed a recently sealed agreement that set tariffs on South Korean goods at 15%, sparing the country from the 25% that Trump had threatened.

The removal of the waiver will have a small impact on the market for semiconductor machinery, according to research from Bernstein. Non-Chinese companies only spent about $2 billion on new gear for their factories in that country in 2024, accounting for less than 2% of total industry sales on equipment last year.

Plants in China owned by overseas companies do have an outsized influence on memory chip supply, though. They account for 10% of computer memory output and 15% of storage chips, according to the report.

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