Verizon Wireless, an American mobile telephone network, has refused to carry text messages from an abortion rights organisation saying it has the right to block “controversial or unsavoury” messages.

The network has been accused of censorship and restricting free speech after turning down a request from Naral Pro-Choice to set up a programme where supporters can ask for regular updates from the campaign group to be sent to their telephones.

The other leading telecommunications companies have accepted the request from Naral, a pro-abortion rights group. Companies are forbidden by law from interfering with voice transmissions on ordinary telephones, but it is thought that text messages fall outside the scope of the law.

The loophole is the latest to come under scrutiny as governments try to ensure that legislation keeps pace with advancing technologies.

Text message services are an increasingly popular way for people to receive news and sport alerts directly to their telephones. Some political groups and charitable organisations have asked supporters to register for campaign alerts by sending a message to a five digit number, known as a short code.

Verizon Wireless, one of the largest wireless networks in the US, has ruled that it will not send messages from the abortion rights group despite potential profits from providing the service.

The wireless network, part owned by the British telecommunications company Vodafone Group PLC, already provides the message service for several Democratic presidential candidates, the Republican National Committee and Amnesty International.

Nancy Keenan, Naral’s president, said the decision should be overturned as it conflicted with the right to freedom of speech.

“No company should be allowed to censor the message we want to send to people who have asked us to send it to them,” Ms Keenan told the New York Times.

“Regardless of people’s political views, Verizon customers should decide what action to take on their phones. Why does Verizon get to make that choice for them?”

Naral supporters pay a small fee to receive messages from the group such as: “End Bush’s global gag rule against birth control for world’s poorest women! Call Congress. (202) 224-3121. Thnx! Naral Text4Choice.”

Jeffrey Nelson, a spokesman for New Jersey-based Verizon, said the entire topic of abortion was prohibited from mass distribution in the company’s code of content. The rulebook bans any campaign “that seeks to promote an agenda or distribute content that, in its discretion, may be seen as controversial or unsavory to any of our users”.

Nelson hinted that the policy could change, as Verizon’s code of content “was initially developed at a time before text-messaging became a mass-market phenomenon”.

“We have been reviewing that code for the last couple of months as text messaging and other multimedia services have become much more mainstream in American communications,” he said.

A spokeswoman for Vodafone in the UK said that the network never intervened to prevent a British customer from signing up to a text alert service, and that companies and organisations were free to offer such services as they wished.

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