Fear of killer robots isn’t just a fear highlighted by sensationalist science fiction moves. Now, several famous scientists and businessmen have called for a ban on AI weapon systems.

In a letter published by the Future of Life Institute, people like Stephen Hawking, Tesla CEO Elon Musk, and linguist Noam Chomsky have signed on to warn against autonomous, weaponized robots.

The academics reason that proliferation of weaponized AI tech could cause a huge spike in terrorism and global instability. They compare military AI to the spread of the AK-47. The cheap assault rifle has become the dominant weapon in everything from small skirmishes to large-scale wars. AI, once it’s developed, would require no expensive, regulated materials and would be relatively cheap to weaponize.

“Artificial Intelligence technology has reached a point where the deployment of such systems is–practically if not legally–feasible within years, not decades,” the letter states. “We believe that AI has great potential to benefit humanity in many ways, and that the goal of the field should be to do so. Starting a military AI arms race is a bad idea, and should be prevented by a ban on offensive autonomous weapons beyond meaningful human control.”

Although fully autonomous weapons aren’t in active use yet, cruise missiles, artillery, and unmanned drones have been equipped with smart guidance systems for several years.

The Future of Life Institute’s letter was presented at the International Joint Conferences on Artificial Intelligence taking place now in Buenos Aires, Argentina.