Four months after receiving a complaint claiming that Verizon "grossly overstated" its 4G LTE coverage in government filings, the Federal Communications Commission has admitted that “at least one carrier” is guilty of a significant rules violation.

The FCC has not named who has been lying but the investigation was apparently triggered by a complaint about Verizon filed in August by the Rural Wireless Association (RWA).

Verizon lied about 4G coverage—and it could hurt rural America, the group said.

The RWA, which represents rural carriers, made its case to the FCC by submitting speed test data. The speed tests showed the Verizon network wasn't providing 4G LTE service in areas that Verizon claimed to cover, according to the RWA.

FCC Chairman Ajit Pai said: "A preliminary review of speed test data submitted through the challenge process suggested significant violations of the Commission's rules."

The FCC said its investigation focuses on "whether one or more major carriers violated the Mobility Fund Phase II (MF-II) reverse auction's mapping rules and submitted incorrect coverage maps".

The FCC last year needed Verizon and other carriers to file maps and data indicating their current 4G LTE coverage in order to help the FCC determine where to distribute up to $4.5 billion in Mobility Fund money over the next 10 years.

The RWA said that Verizon "fil[ed] a sham coverage map as a means of interfering with the ability of rural carriers to continue to receive universal service support in rural areas." Verizon denied any wrongdoing at the time, saying "we are confident that our Mobility Fund map is fully consistent with the FCC's mapping specifications."