News Corporation has threatened to restrict its top-rated Fox TV channel to subscribers if an internet startup wins a battle for the right to stream US broadcast networks online.

Hits including American Idol, The Following, Glee and X Factor have made Fox the number-one network for the last eight years. But speaking at the National Association of Broadcasters event in Las Vegas, its president, Chase Carey warned he would consider scrapping its open broadcast if a New York-based startup is allowed to retransmit its shows without paying a license fee.

Aereo, backed by media turned internet mogul Barry Diller, is at loggerheads with major media firms including News Corp, CBS, Disney and others over its service which delivers TV over the web. Subscribers pay $12 month to stream live broadcasts of TV channels on mobile devices. Aereo does not pay fees to the media companies whose programmes it redistributes.

Earlier this month the company won an appeal against its critics attempts to block the service, which is so far limited to New York. It was Aereo's second victory against the major media groups. Subscribers are allocated their own antennae, a move that the majority of appeal judges ruled meant the service was legal. One dissenting judge, however, called the service a "sham" and was abusing a loophole in the law. The media firms are planning further action.

"Aereo is stealing our signal," Carey said in his keynote conversation at the NAB. "We believe in our legal rights. We're going to pursue those legal rights fully and completely, and we believe we'll prevail. But we want to be clear. If we can't have our rights properly protected through legal and political avenues, we will pursue business solutions. One such business solution would be to take the network and turn it into a subscription service."

In a statement issued after the NAB speech, Carey said Fox would not "just sit idle and allow our content to be actively stolen".

"We simply cannot provide the type of quality sports, news, and entertainment content that we do from an ad supported only business model. We have no choice but to develop business solutions that ensure we continue to remain in the driver's seat of our own destiny. One option could be converting the Fox broadcast network to a pay channel, which we would do in collaboration with both our content partners and affiliates," he said.

Virginia Lam as a spokesperson for Aereo, said: "Aereo has invented a simple, convenient way for consumers to utilize an antenna to access free-to-air broadcast television, bringing television access into the modern era for millions of consumers. It's disappointing to hear that Fox believes that consumers should not be permitted to use an antenna to access free-to-air broadcast television.

"Over 50 million Americans today access television via an antenna. When broadcasters asked Congress for a free license to digitally broadcast on the public's airwaves, they did so with the promise that they would broadcast in the public interest and convenience, and that they would remain free-to-air. Having a television antenna is every American's right."