In March, Gizmodo revealed that Google was working with the Defense Department to develop artificial intelligence for analyzing drone footage as part of an initiative known as Project Maven.

Google’s involvement sparked ethical concern and anger among employees, Gizmodo initially reported. An internal petition called on Google CEO Sundar Pichai to cancel Project Maven and “[d]raft, publicize, and enforce a clear policy stating that neither Google nor its contractors will ever build warfare technology.” The New York Times reported in April that over 3,000 Google employees signed the petition.

Now, according to Gizmodo, “about a dozen” Google employees are resigning due to Project Maven. Their reasons for leaving range from lack of transparency to ethical concerns. “Over the last couple of months, I’ve been less and less impressed with the response and the way people’s concerns are being treated and listened to,” an unidentified employee who resigned told Gizmodo.

For its part, Google says that its Pentagon contract is only a test and that it covers non-classified images.

“The technology flags images for human review, and is for non-offensive uses only,” a Google spokesperson told Gizmodo in March. “Military use of machine learning naturally raises valid concerns. We’re actively discussing this important topic internally and with others as we continue to develop policies and safeguards around the development and use of our machine learning technologies.”

Still members of the tech industry are concerned. In addition to the Google-specific internal petition, there is a broader petition targeting IBM, Microsoft, Amazon and Google, created by tech workers who “believe that tech companies should not be in the business of war.”

Researchers who are critical of Google also posted an open letter worrying about Google providing the Pentagon with “open source ‘deep learning’ technology” along with engineering expertise.

“The DoD contracts under consideration by Google, and similar contracts already in place at Microsoft and Amazon, signal a dangerous alliance between the private tech industry, currently in possession of vast quantities of sensitive personal data collected from people across the globe, and one country’s military,” the letter states. “They also signal a failure to engage with global civil society and diplomatic institutions that have already highlighted the ethical stakes of these technologies.”

In October of 2017, over 100 companies attended an industry event related to Project Maven, according to the Defense Department.

Fortune contacted Google for comment about these resignations and will update this post if it responds.

Project Maven was started in April of 2017 by then-Deputy Defense Secretary Bob Work, who started an Algorithmic Warfare Cross-Functional Team. “The project’s first task involves developing and integrating computer-vision algorithms needed to help military and civilian analysts encumbered by the sheer volume of full-motion video data that DoD collects every day in support of counterinsurgency and counterterrorism operations,” according to a Defense Department article from 2017.