T-Mobile is asking the FCC to consider reserving half or more of the 600 MHz spectrum cleared for auction for smaller carriers to bid on.

In an FCC filing, T-Mobile said adjusting the spectrum reserve based on different clearing scenarios would “promote robust competition among service providers and ensure the continued vitality of four nationwide providers.”

The FCC had pledged to set aside up to 30 MHz of spectrum in the incentive auctions for bidders without large low-band spectrum holdings. The limitations would primarily prevent AT&T and Verizon from bidding on the reserves.

Under T-Mobile’s new proposal, the spectrum reserve could be as large as 50 MHz. The carrier reasons that 20 MHz (10x10 MHz) blocks are ideal for low-band spectrum deployments but, under the current reserve plan, only one competitive carrier could potentially secure that amount of low-band spectrum.

The carrier also argues that by reducing the reserve to 20 or 10 MHz in smaller clearing scenarios, the FCC “effectively preserves the right of AT&T and Verizon to divide the unreserved spectrum and acquire twenty megahertz each.” In order to compete in those scenarios, T-Mobile argues that smaller carriers will have to risk be closed out by AT&T and Verizon.

The FCC’s current spectrum reserve plan has garnered criticism from the large carrier. After the FCC proposed the reserves earlier in the year, AT&T threatened to sit out the incentive auctions since the rules could restrict it from bidding in markets covering more than 70 percent of the population.

As it stands, AT&T has reportedly set aside $9 billion for bidding in the auctions—scheduled for 2015. That earmark was almost eclipsed by a reported $10 billion that T-Mobile and Sprint wanted to pool together for joint bidding. U.S. regulators voiced opposition to such a joint venture.