The largest US mobile phone company has began legal action against new government regulations that protect the free flow of internet traffic in the latest twist on the "net neutrality" debate.

Verizon Communications is taking the action following the publication last week of new Federal Communications Commission rules barring fixed-line broadband companies from prioritising or blocking any legal content on their networks.

Some companies would like to charge content producers in exchange for delivering their material, such as movies, to consumers faster than other non-paying internet traffic.

The rules, which come into effect in two months, are more lenient on mobile networks. Phone companies are only barred from blocking voice and other applications that compete with their own services, but are allowed to manage all other traffic so that their systems are not overwhelmed.

Nonetheless, Verizon is challenging the FCC's right to set rules on net neutrality. "We are deeply concerned by the FCC's assertion of broad authority to impose potentially sweeping and unneeded regulations on broadband networks and services and on the internet itself," said Michael Glover, Verizon's general counsel.

"We believe this assertion of authority is inconsistent with the statute and will create uncertainty for the communications industry, innovators, investors and consumers."

The challenge was expected. Following approval of the FCC's open internet regulations in December, Verizon filed a similar suit earlier this year, which was thrown out after the court determined the complaint was premature. Publication of the rules on 23 September in the Federal Register gave Verizon its opportunity to mount a fresh challenge.

The rules are illegal because they would modify Verizon's existing spectrum licenses without its approval, the company said in a notice of appeal filed on Friday at the US district court of appeals in Columbia.

Those arguing for an open internet say the FCC rules do not go far enough, giving mobile carriers too much freedom to throttle traffic. Media reform group Free Press filed a suit in a Boston appeals court on Wednesday arguing the regulations were too weak.

"When the FCC first proposed the open internet rules, they came with the understanding that there is only one internet, no matter how people choose to reach it," said Free Press policy director Matt Wood.

"The final rules provide some basic protections for consumers, but do not deliver on the promise to preserve openness for mobile internet access. They fail to protect wireless users from discrimination, and they let mobile providers block innovative applications with impunity."