Internet firms have warned that government plans to monitor email and social media use in Britain are liable to be used by repressive regimes elsewhere in the world to justify their state surveillance.

No internet business was willing to offer a public criticism of the coalition's proposal on Monday, but many privately raised fears over the legalising of a power to see who is contacting whom online in real time.

"There is a question of jurisdiction. There is a risk that if you offer this access to [the authorities in] Britain, then you have to offer it to countries like Syria and Bahrain," said an internet industry official who declined to be identified because the proposal has not been outlined in detail.

A number of MPs and civil liberties groups argued that the plan would endanger privacy and unfettered free expression online. Julian Huppert, the Lib Dem MP, said on Twitter that the Commons home affairs committee wanted to call the home secretary, Theresa May, to give evidence on the proposal. More than 14,000 people have signed a petition by the internet advocacy body Open Rights Group.

The proposal is expected to be outlined in the Queen's speech on 9 May; it allows the authorities to have "on demand" access to online traffic in real time. However, the security minister, James Brokenshire, said the purpose was solving crime not "real-time snooping on everybody's emails". He told BBC Radio 4's World at One: "We absolutely get the need for appropriate safeguards, and for appropriate protections to be put in place around any changes that might come forward.

"What this is not is the previous government's plan of creating some sort of great big Big Brother database. That is precisely not what this is looking at."

One official familiar with the plan said the government wanted to bring social networks, such as Twitter and Facebook, "broadly into line" with existing legislation covering the surveillance of phone calls. Authorities would not be able to read the content of messages without an intercept warrant issued by the home secretary under the Regulation of Investigatory Powers Act 2000 (RIPA)..

The Home Office is understood to have outlined its plans at a meeting in January with the Internet Service Providers' Association, which represents companies including Google and BT, after a series of high-level meetings with the government intelligence agency GCHQ. No detailed proposal has been seen by the association; it was given only an outline of what the government hopes to introduce.

Internet companies are anxious to learn what they will be required to do. Internet service providers, such as BT and TalkTalk, could be required to install systems to harvest so-called packet data from internet communications, so security officials will be able to see who is visiting which websites and talking to whom. "We haven't seen full proposal yet and we are hoping for more information from the Home Office soon … It appears to be something we would have to look very carefully at," said one industry official.

Another official suggested that stronger powers to secretly monitor internet communication could compromise the government's bid for transparency.

But the backlash over the plan has been capitalised on by some internet firms. The makers of Tor, the internet anonymity shield used by activists in Iran and China, said that it would support users who wished to evade detection by UK authorities.

Andrew Lewman, the director of Tor, compared the UK plan to the data retention laws in Germany that require internet providers to log users' website visits. He said use of Tor rose after that law was introduced.

"Once the data is collected, regardless of the current intentions, it will be used for all sorts of reasons over time," Lewman told the Guardian. "The number of crimes will expand to include all sorts of petty issues, political repression, and restrictions on speech. Eventually someone will think they can predict crime before it happens by using the data."

The Association of Chief Police Officers said: "Telecommunications technology is changing rapidly; there is a need to look at how we can ensure the capability to investigate crime, save lives and prosecute offenders is maintained. It is a matter for government to ensure the right boundaries are set so that our approaches are justified, necessary and proportionate."

A Home Office spokeswoman said: "It is vital that police and security services are able to obtain communications data in certain circumstances to investigate serious crime and terrorism and to protect the public. We need to take action to maintain the continued availability of communications data as technology changes.

"Communications data includes time, duration and dialling numbers of a phone call, or an email address. It does not include the content of any phone call or email, and it is not the intention of government to change the existing legal basis for the interception of communications."