Tech CEOs have plenty of reasons to worry about public attention these days, but usually not during their big product events. Tim Cook tends to be giddy when he opens the Apple Event each September. Facebook still makes a big deal about F8, where Mark Zuckerberg once gave everyone in the audience an Oculus VR headset to wear as he walked past them unseen. These events are moments for celebration, not hyperscrutiny: Tech writers who focus on gear scramble to keep up with all the exciting new announcements that gadget-buyers want to get the scoop on.

But when Microsoft CEO Satya Nadella takes the stage at the Mobile World Congress in Barcelona, Spain, this weekend to unveil the new augmented reality headset HoloLens 2, he may have a worry on his mind: Many of his employees are outraged over a $479 million contract the company inked last November with the U.S. military to use the new HoloLens in a platform that “provides increased lethality, mobility, and situational awareness necessary to achieve overmatch against our current and future adversaries.” On Friday, Microsoft employees sent a letter to Nadella and Microsoft President Brad Smith saying that they “refuse to create technology for warfare and oppression” and demanding that Microsoft cancel the contract and stop developing weapons technologies going forward. More than 50 employees have signed the document so far.

On behalf of workers at Microsoft, we're releasing an open letter to Brad Smith and Satya Nadella, demanding for the cancelation of the IVAS contract with a call for stricter ethical guidelines.

If you're a Microsoft employee you can sign at: https://t.co/958AhvIHO5 pic.twitter.com/uUZ5P4FJ7X — Microsoft Workers 4 Good (@MsWorkers4) February 22, 2019

If your goal is to sell lots of HoloLens devices to consumers and companies, the timing of this employee letter stings. No one wants to discuss military contracts while making a pitch at Mobile World Congress. Attempting to force such conversations during a new product launch suggests that tech workers concerned about their employers’ activities have another lever to pull.

The last year has seen a growing cadre of tech employees engaging in collective action to force large technology companies to act more ethically. Perhaps most famously, there were the Google employees who walked out to demand an end to forced arbitration for workers who experience sexual harassment or discrimination at the company—a movement that culminated, this week, with Google announcing it is ending the practice for all employees. By sharing this letter right before a major product event, with a very specific illustration of how HoloLens tech is being sold for military purposes, employees are showing they’re willing to undermine the celebratory moments for the company. It’s a strategy that’s riskier for them, but potentially more painful for their bosses, too.

This goes a step further than presenting a letter or internal petition to management, though that can certainly work. Google, for example, ended a Department of Defense contract to build artificial intelligence for drone technology after employee outcry. By voicing similar demands in advance of one of the biggest international tech conferences of the year, Microsoft employees are politicizing the company’s narrative about a cool new product. It’s not quite the same as a dropping a banner or chanting while their boss has the mic, but it does generate press, and it could complicate the decision for some new customers and firms to buy in.

This isn’t the first time Microsoft employees have demanded their employer terminate contracts with U.S. government agencies doing work they found appalling. In June of last year, more than 100 employees signed an open letter to Nadella demanding Microsoft stop working with Immigration and Customs Enforcement over the Trump administration’s family separation policy at the border. By July, 500 employees had signed on. Microsoft responded by saying that it’s not aware that the services it provides to ICE are being used to separate families at the border, adding that the company is “dismayed by the forcible separation of children from their families.” But the contracts were never terminated.

This time, however, Microsoft can’t say it doesn’t know how its tech is being used. The contract the company signed with the military makes it clear that the HoloLens will help “increase lethality.” As the letter from Microsoft employees argues, “as employees and shareholders, we do not want to become war profiteers.” Their point is they don’t want to build tech that they thought would be used for more humane purposes, like helping doctors perform surgery or architects design buildings, to end up also inside platforms that assist in killing people. Pointing out all of this during a major, global product announcement doesn’t only make the technology feel toxic to potential customers—it could make working on such technology toxic to future prospective workers at Microsoft, too. And losing talent is a lot more painful for Microsoft than selling fewer AR sets.