The Federal Trade Commission (FTC) has filed a lawsuit to block Nvidia’s attempt to purchase Arm.

Arm is one of the world’s most important semiconductor design companies. Unlike Intel or AMD, Arm designs and licenses its semiconductors to clients, who are then responsible for manufacturing them. Apple, Qualcomm, Nvidia, Samsung and others are among Arm’s customers.

Nvidia announced its plans to purchase Arm in September 2020 for $40 billion, a move that immediately drew criticism throughout the industry. Many worried that Nvidia would keep Arm’s greatest innovations for itself, ending Arm’s long-standing practice of maintaining strict neutrality and licensing its designs to anyone willing to pay.

The EU has already launched an investigation into the deal, and UK regulators have signaled they may try to block it. Now the FTC has filed a lawsuit to prevent the deal from happening.

“The FTC is suing to block the largest semiconductor chip merger in history to prevent a chip conglomerate from stifling the innovation pipeline for next-generation technologies,” said FTC Bureau of Competition Director Holly Vedova. “Tomorrow’s technologies depend on preserving today’s competitive, cutting-edge chip markets. This proposed deal would distort Arm’s incentives in chip markets and allow the combined firm to unfairly undermine Nvidia’s rivals. The FTC’s lawsuit should send a strong signal that we will act aggressively to protect our critical infrastructure markets from illegal vertical mergers that have far-reaching and damaging effects on future innovations.”

Given the headwinds Nvidia is facing, a deal to acquire Arm is looking increasingly unlikely.