Verizon and MetroPCS have laid out their argument against the FCC's net neutrality regulations in a brief filed yesterday with a federal appeals court.

The brief is part of the operators' ongoing 18-month legal challenge to the regulations, which stop wireless providers from blocking lawful websites and competing over-the-top applications like Skype.

Calling the regulations "arbitrary and capricious," the companies argued that the rules should be overturned because they conflict with the Communications Act, are outside the FCC's authority and violate constitutional rights.

"They subject broadband providers to quintessential common-carrier duties by compelling them to carry the Internet traffic of all comers, and to do so at a uniform, nondiscriminatory price of zero," Verizon and MetroPCS said.

The suit is being heard in the U.S. Court of Appeals for the District of Columbia, the same court that ruled in 2010 that the FCC lacked the authority to require broadband Internet providers to treat all Web traffic equally. The legal setback did not stop the agency from pushing forward with its net neutrality plans, and at the end of that year, the FCC passed its open Internet order on a narrow 3-2 vote.

If the challenge is successful and the court tosses out the regulations, wireless and broadband Internet providers could be allowed to block online content and competing services. The case against Comcast, which led to the current legal battle, stemmed from the cable operator's decision to slow traffic to file-sharing website BitTorrent.

The regulations also require broadband Internet providers to disclose information about their network management practices.

The Communications Act forbids the FCC from applying common-carrier regulation to broadband providers. Verizon and MetroPCS argued the net neutrality regulations did just that by forcing them to carry all lawful Internet traffic. The companies also argued that the FCC doesn't have authority to impose the rules because none of the provisions cited in its order "expressly authorizes these rules."

The regulations also are unconstitutional by violating First Amendment free speech rights and Fifth Amendment protections that shield businesses "from government compulsion to turn over their private property for use by others without compensation," the companies claimed.

An FCC spokesman said the agency looks "forward to defending our open Internet rules in court."

“This strong and balanced framework is helping ensure that the Internet continues to thrive as an engine for innovation, investment, job creation and free expression,” he said.

The FCC’s response to the brief is due in September.

The two operators first filed suit against the regulations early last year, only to have the complaint dismissed on a technicality. The suit was re-filed, and the court in March allowed the challenge to proceed after dismissing the FCC’s request for a delay.