Tech firms and universities interested in building AI-powered weapons for lucrative military contracts are, predictably, facing some significant pushback.

The news: A letter circulating at Google, signed by thousands of employees, protests the company’s involvement in creating technology for the Defense Department, according to the New York Times. The letter comes after Gizmodo and the Intercept both revealed that Google was giving the Pentagon special access to its machine-learning software to help analyze images from drones.

Also: A group of 50 leading AI researchers is boycotting Korean university KAIST over its plan to develop autonomous weapons, reports the Verge. The university announced in February that it was launching a joint research center with South Korean defense company Hanwha Systems.

There’s more: Other projects exist. Russian weapons maker Kalashnikov is developing combat robots, and China’s plans for armed autonomous submarines were leaked earlier this month, for instance.

Why it matters: Autonomous weapons could easily enough become a reality, but determining whether using them is a good idea is fraught with tricky ethical arguments—on both sides. There is a campaign to ban autonomous weapons, but so far it’s had little success in halting their development.