Chip designer Nvidia (NVDA, $139.37) said that US officials told it to stop exporting two top computing chips for artificial intelligence work to China, a move that could cripple Chinese firms’ ability to carry out advanced work like image recognition. Nvidia shares fell 6.6% after hours. The company said the ban, which affects its A100 and H100 chips designed to speed up machine learning tasks, could interfere with the completion of developing the H100, the flagship chip it announced this year.

Nvidia said it had booked $400 million in sales of the affected chips this quarter to China that could be lost if firms decide not to buy alternative Nvidia products. It said it plans to apply for exemptions to the rule. Only last week it forecast a sharp drop in revenue for the current quarter on the back of a weaker gaming industry. It said it expected third-quarter sales to fall 17% from the same period last year.

Without American chips from companies like Nvidia and AMD (AMD, $82.33), Chinese organizations will be unable to cost-effectively carry out the kind of advanced computing used for image and speech recognition, among many other tasks.