Leading human rights groups including Amnesty International and Index on Censorship have written to the home secretary, Theresa May, expressing concerns about a potential clampdown on social networks following the riots a fortnight ago.
The coalition of 10 human rights and free speech advocates said they were "very concerned" that new measures to curb Facebook and Twitter would be "susceptible to abuse" and "undermine people's privacy".
Facebook, Twitter and BlackBerry maker Research in Motion are expected face down ministers' calls to restrict social networking in times of civil unrest at a Home Office summit on Thursday lunchtime.
For their part, May and the minister for security, James Brokenshire, are expected to row back on the prime minister's calls for suspected rioters to be banned from social networks in times of civil unrest at Thursday's meeting.
They are instead expected to discuss how law enforcement could better use Twitter and Facebook in emergencies.
"As you know, there is existing legislation regulating the interception and disclosure of communications information, the use of communications evidence by law enforcement and restrictions on people's use of communications technology," the open letter said.
"It is reasonable to review the existing legal regime to ensure that it appropriately fits new technologies.
"However, turning off, restricting or monitoring people's communications networks are matters that require extreme care and open, detailed deliberation."
The letter follows a study of riot-related tweets, compiled by the Guardian, that has cast doubt on the rationale behind David Cameron's recent proposal to ban potential rioters from Twitter and Facebook.
Representatives of the 10 leading human rights groups, including Brett Solomon, the executive director of Access, and Mike Blakemore, the media director of Amnesty UK, have signed the letter to May.
"We are very concerned that new measures, made in good faith but in a heated political environment, will overextend powers in ways that would be susceptible to abuse, restrict legitimate, free communication and expression and undermine people's privacy," they said.
"This is especially so if proposals involve unaccountable voluntary arrangements between law enforcement and communications providers."
The human rights groups have requested a meeting with the home secretary to discuss the government's plans.
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