By Marina Lopes San Antonio (Reuters) – The U.S. Federal Communications Commission is still considering caps on the amount of spectrum a single carrier will be allowed to acquire in a 2015 spectrum auction, the commissions wireless bureau chief said on Tuesday. The caps would most likely affect the two biggest U.S. carriers, ATT and Verizon, and would give smaller carriers a better chance to compete for a portion of frequencies under one gigahertz, valued for their strength and reach. In April 2013, the U.S. Justice Department urged the FCC to devise an auction that would help ensure smaller carriers obtained a fair share of that spectrum. The so-called incentive auction will give TV stations that currently own the valuable frequencies the opportunity to voluntarily give up their frequencies to the FCC.