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(Bloomberg) -- China’s top chipmaker, Semiconductor Manufacturing International Corp., warrants investigation as the company appears to have violated US sanctions by supplying components to Huawei Technologies Co., US lawmakers said.

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“It sure looks like it did” violate sanctions, Representative Michael McCaul said Wednesday at a briefing at the US embassy in the Hague. SMIC continues “to try to get our intellectual property.”

Huawei uses an advanced 7-nanometer processor built by SMIC to power its latest smartphone, a teardown commissioned by Bloomberg News showed, indicating that China is making headway in its push to produce cutting-edge semiconductors despite US sanctions. SMIC’s shares slid as much as 7.4% in Hong Kong, its biggest fall in more than three months. Its Shanghai stock dived as much as 8.6%.

Existing rules require any company that intends to supply Huawei with US technology, which is present throughout SMIC’s operations, to get approval from Washington. It’s unclear whether SMIC has a US license to supply Huawei.

McCaul, Republican chairman of the House Foreign Affairs Committee, has been vocal in protesting what he considers insufficient enforcement of the Entity List, which is enforced by the Commerce Department’s Bureau of Industry and Security and specifies license requirements imposed on restricted exports. Neither McCaul nor his committee have much direct sway over sanctions.

Representative Mike Gallagher, chairman of the House Select Committee on Competition with China, picked up on the theme, suggesting the US should end all its exports to both Huawei and SMIC — even those involving older technology that are currently allowed under the law.

“The time has come to end all U.S. technology exports to both Huawei and SMIC to make clear any firm that flouts US law and undermines our national security will be cut off from our technology,” Gallagher said in a statement.

Read more: What Huawei’s Comeback Says About US-China Tech War: QuickTake

Although Congress can call officials from the BIS to Capitol Hill to explain export control policy, officials across administrations have shared information on potential new controls only sparingly, citing national security concerns.