T-Mobile, once the smallest of four national telecom carriers, is now on the road to dominate 5G spectrum to the concern of AT&T and Verizon, which have complained to the Federal Communications Commission. In August, Verizon petitioned the FCC to reassess its greenlight for a new lease that would give T-Mobile an additional 10MHz to 30MHz in the 600MHz band in 204 counties. AT&T just added its voice, with a filing supporting Verizon’s point of view. T-Mobile’s purchase of Sprint made it one of now three major carriers.

Ars Technica reports that, “T-Mobile also bolstered its low-band spectrum holdings by dominating a 600MHz auction in 2017.” In its filing, AT&T wrote that, “the combination of Sprint and T-Mobile … exceeds the Commission’s spectrum screen, often by a wide margin, in Cellular Market Areas representing 82 percent of the U.S. population,” adding that “additional spectrum leases with Dish will cause T-Mobile to exceed the 250MHz screen by as much as 136MHz.”

Verizon said that, “T-Mobile already holds licenses for 311MHz of low- and mid-band spectrum nationwide … more than the low- and mid-band spectrum licensed to Verizon and AT&T combined.”

The FCC’s spectrum screen is not a hard-and-fast limit, notes Ars Technica, “but, rather, one data point the FCC uses in its public-interest analyses.” Channel 51 License Company and LB License Co, T-Mobile’s new 600MHz band leases, “do not provide any service over the spectrum.” Still, AT&T and Verizon told the FCC that this accumulation of spectrum has a “high likelihood” of creating “competitive harms.”

T-Mobile countered Verizon’s complaints by saying that, “as a company that elected not to participate in the Commission’s 600MHz auction and currently touts its massive millimeter-wave spectrum holdings as support for 5G superiority, it is simply disingenuous for Verizon to now complain that T-Mobile’s addition of 600MHz spectrum to its portfolio is somehow anticompetitive.”

T-Mobile added that its spectrum will, instead, create more competition for “sorely needed in-home wireless broadband in competition with Verizon — particularly in rural areas.”

Light Reading explains that the FCC’s “spectrum screen,” set up in 2004, is “designed to trigger an investigation by the FCC if an operator moves to purchase more than one-third of the total amount of spectrum available in a given market,” but that the agency “has rarely used the screen as a basis to prevent spectrum purchases.”

Instead, Light Reading suggests that “what AT&T and Verizon are really worried about is that T-Mobile is going to wreak havoc in the upcoming C-band spectrum auction, forcing AT&T and Verizon to spend billions of dollars in extra money to ensure they gain critical mid-band spectrum for 5G.”

T-Mobile chief executive Mike Sievert said that he thinks “AT&T and Verizon will absolutely kill each other over C-band” by spending “tens of billions of dollars they don’t have to stress out their balance sheets and put at risk their share buyback and dividend plans in order to not be left out of the party on 5G.” T-Mobile, he added, is interested in that spectrum but, said Sievert, “we’re coming from a position of strength and a tradition of being disciplined.”