AT&T is trying to block T-Mobile’s plan to use SpaceX’s Starlink satellite network to expand its mobile service.

The Federal Communications Commission asked for public comment on T-Mobile’s SpaceX plan last month. AT&T and its affiliates filed a complaint Thursday, asking the agency to stop the plan and saying it could “jeopardize or inhibit” its wireless and mobile broadband services. 

AT&T has spectrum rights adjacent to the range that SpaceX would be using for this plan, which would require the latter to modify its license for its network of orbiting satellites to receive and broadcast signal to and from mobile devices. SpaceX would use the so-called PCS G-Block of signal bands that are between the 1.9GHz and 2GHz range, according to Ars Technica, which reported the story earlier Friday.

SpaceX has requested waivers to use this signal range. AT&T says its proposal doesn’t do enough to prevent interference with other networks, saying in its filing that SpaceX’s “technical showings are woefully insufficient regarding the risk of harmful interference posed by their planned [supplemental coverage from space] deployments.”

Though SpaceX and T-Mobile haven’t publicized a successful call from space that would demonstrate the plan’s lack of interference, AT&T noted that it has already made a surface-through-space call with its satellite partner AST SpaceMobile. 

AT&T hasn’t announced when its own consumers will see the benefit of its satellite partnership with AST, which aims to augment regular 5G service. It has the advantage that AST has been connecting satellite calls for years, while SpaceX’s network of microsatellites will need approval before they can carry calls. Verizon had also announced that it would use Amazon’s Project Kuiper satellites (none of which has been launched into orbit yet) to expand its mobile network. 

Meanwhile, Apple’s Emergency SOS system available only on the latest iPhone 14 series has been the only widely available satellite-to-cell system in use so far. Qualcomm’s Snapdragon Satellite service is expected to go live later this year for phones using the latest Snapdragon chips.

Neither AT&T nor T-Mobile immediately responded to a request for comment.