"Discriminating in providing mobile services is contrary to the principles which have governed both wired and wireless carriers for decades," the organizations argued in a petition filed Tuesday.

Public Knowledge and Free Press are spearheading the effort, while six other groups--Consumers Federation of America, Consumers Union, EDUCAUSE, Media Access Project, New America Foundation and U.S. Public Interest Research Group--have signed on to the petition. The groups are urging the FCC to ban mobile carriers from "engaging in unjust and unreasonable discrimination in providing text messaging services."

With more and more consumers relying on text messaging, advocates say it's critical to stop telecoms from blocking messages. "There's a lot at stake because this is the way people are communicating now," said Gigi Sohn, president and co-founder of Public Knowledge. The groups argued to the FCC that declining to transmit messages from certain senders violates common carrier rules, which prohibit telephone companies from picking and choosing which conversations to allow.

On at least two occasions this year, wireless companies refused to send certain text messages. In September, Verizon barred the abortion rights group NARAL Pro-Choice America from sending messages to supporters, even though they had signed up to receive them. The company reversed its decision after an article about the situation ran in The New York Times. And earlier this year, several carriers refused to run text messages from a rival, Rebtel, that offers Voice over Internet Protocol service.

The NARAL incident in particular sparked fears that telecoms and other service providers could effectively choke digital communication. "Letting cell phone providers decide to block certain groups from sending messages raises huge concerns about their power," said Catherine Sandoval, a professor at Santa Clara University School of Law.

What NARAL is doing is the purest form of political speech, Sohn added. What's more, she said, First Amendment free speech principles--which typically restrict the governments' ability to censor people--might also apply to telecoms. "They're certainly supposed to be acting as public trustees of the airwaves, so when they block this kind of speech, there are First Amendment implications," she said.

Verizon did not return calls.

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