(Bloomberg) -- The U.S. Federal Communications Commission, proclaiming a new front in the fight against automated nuisances, plans to clarify that telephone companies may block unwanted text messages.

The agency is set to vote Wednesday on a measure that supporters say would maintain and strengthen the legal foundation that allows phone companies to cut off unwanted messages. The change will clear up the regulatory status of text messages, which had been unclear.

The move is a loss for messaging company Twilio Inc. and free speech groups that had asked for more protections for text messages, saying carriers sometimes interfered.

Nine Democratic U.S. senators and Vermont’s Bernie Sanders, an independent, in a Dec. 7 letter asked the FCC not to take the step, saying it would let phone companies “block any text message they wish” and charge more to businesses trying to reach clients and consumers.

FCC Chairman Ajit Pai, who leads a Republican majority at the agency, said in a Nov. 20 statement that the vote would “make clear that wireless providers are authorized to take measures to stop unwanted text messaging” and help “prevent a flood of spam robotexts from clogging Americans’ phones.”

Opponents of the move said carriers already have the ability to block unwanted texts, and might abuse the power to censor speech.

“This action undermines the public’s right to use text messaging without undue interference from wireless companies,” the policy group Public Knowledge said in a Dec. 5 statement.

Top U.S. carriers back the plan. “The FCC’s proposal is a big win for consumers,” said Scott Bergmann, senior vice president with the CTIA trade group that represents AT&T Inc. and Verizon Communications Inc. “Today, more than 50 percent of emails are spam, and no one wants their texts to look like their email inbox.”

The spam rate for plain text messages is about 2.8 percent, according to a CTIA estimate.

Wireless providers have blocked messages and imposed content restrictions, Twilio said in its petition to the FCC in 2015. Twilio’s products help corporations including Uber Technologies Inc., and Airbnb Inc. to send automated text messages to consumers.

Policy groups sought protection for text messages after Verizon in 2007 rejected a request by Naral Pro-Choice America to sign up members to receive text messages that encourage people to support abortion rights legislation. After protests, Verizon reversed that decision and called it incorrect.

To contact the reporter on this story: Todd Shields in Washington at tshields3@bloomberg.net

To contact the editors responsible for this story: Jon Morgan at jmorgan97@bloomberg.net, John Harney

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