A U.S. cybersecurity company says it has evidence hackers linked to the Chinese government may have tried to violate a recent agreement between Washington and Beijing not to hack private firms in each other’s country for economic gain.

The firm, CrowdStrike Inc., plans to announce Monday that unnamed customers in the technology and pharmaceutical industries have faced attempted—though unsuccessful—intrusions from China-linked hackers. Two incidents took place the day before and the day after President Barack Obama and Chinese President Xi Jinping said on Sept. 25 they reached an “understanding” not to use cyberspies to commit economic espionage against each other, according to CrowdStrike.

The Chinese embassy in Washington didn’t immediately respond to a request for comment.

“We are aware of this report. We’ll decline comment on its specific conclusions,” said a senior Obama administration official. “We have and will continue to directly raise our concerns regarding cybersecurity with the Chinese.”

American companies have complained for years that Beijing-linked hackers have sought to pilfer their trade secrets from corporate computers. U.S. spies have hacked into Chinese companies, such as Huawei Technologies Co., though American officials have argued such hacks are for national security purposes and not to steal trade secrets.