Google is getting serious about its Cardboard VR initiative, at least on the trademark front: The company has removed a number of apps over the use of the Cardboard moniker this week, informing developers that their listings violated Google Play’s content policy.

Some of the affected apps included Cardboard VNC, Cardboard Theater and Cardboard Catapult. At least one of the affected developers has since responded by renaming his app to VR Theater for Cardboard.

Google first released Cardboard as a free VR viewer at its Google I/O developer conference in 2014. At the time, many took it as Google making fun of Facebook spending $2 billion for Oculus. But Google has continued to invest in Cardboard, striking partnerships with GoPro and others to develop production tools for virtual reality content, and most recently adding Cardboard support to Google Street View.

Google has made specs for Cardboard hardware, which uses mobile phones as displays, freely available online, and encouraged third-party companies to build their own Cardboard-compatible headsets. Earlier this year, Google unveiled a “works with Cardboard” seal of approval for third-party hardware. It’s possible that Google could also start to go after hardware manufacturers that make too liberal use of the Cardboard trademark.

Google didn’t immediately respond to a request for comment.