The data protection watchdog will press for "limitations and safeguards" to protect citizens' privacy from Government proposals to monitor all calls, emails, texts and website visits.
Information Commissioner Christopher Graham wants assurances about plans that will mean internet companies are instructed to install hardware tracking telephone and website traffic.
The legislation, expected in next month's Queen's Speech, will enable GCHQ to access information "on demand" in "real time" without a warrant.
A spokesman for the Information Commissioner's Office said: "The Information Commissioner's role in this Home Office project, both under this government and the last, has been to press for the necessary limitations and safeguards to mitigate the impact on citizens' privacy.
"We will continue to seek assurances, including the implementation of the results of a thorough Privacy Impact Assessment (PIA).
"Ultimately, the decision as to whether to proceed with the project is one which has to be taken by Parliament."
Downing Street insisted only data - times, dates, numbers and addresses - not content would be accessible as it sought to quell fears about the proposals amid a fierce backlash from its own backbenchers as well as civil liberties groups.
A previous attempt to introduce a similar law was abandoned by the former Labour government in 2006 in the face of fierce opposition from the Conservatives and the Liberal Democrats.
David Davis, Conservative former shadow home secretary, said: "This needs to be done because it can be done - that's been the attitude of many 'securocrats' over the ages.
"This is not necessary, you can do it under control of the law. What is proposed is completely unfettered access to every single communication you make. This argument it doesn't cover content - it doesn't cover content for telephone calls, but your web address is content. If you access a web (site), that is content."
Deputy Prime Minister Nick Clegg defended the plans, insisting he was "totally opposed" to the idea of governments reading people's emails at will.
He added: "The point is we are not doing any of that and I wouldn't allow us to do any of that.
"I am totally opposed to it as a Liberal Democrat and someone who believes in people's privacy and civil liberties.
"All we are doing is updating the rules which currently apply to mobile telephone calls to allow the police and security services to go after terrorists and serious criminals and updating that to apply to technology like Skype which is increasingly being used by people who want to make those calls and send those emails."
Security minister James Brokenshire said the emphasis was on solving crime rather than "real-time snooping on everybody's emails".
But Isabella Sankey, Liberty's director of policy, said: "Whoever is in government, the grand snooping ambitions of security agencies don't change.
"Proposals to stockpile our web, phone and texting records were shelved by Labour. Now we see plans to recycle this chilling proposal leaking into the press."
Nick Pickles, director of the Big Brother Watch campaign group, said: "No amount of scare-mongering can hide the fact that this policy is being condemned by MPs in all political parties.
"The Government has offered no justification for what is unprecedented intrusion into our lives, nor explained why promises made about civil liberties are being casually junked."
No 10 said proposals were included in its Strategic Defence and Security Review (SDSR) in 2010.
The Prime Minister's official spokesman said: "Communications data is used currently in 95% of all serious crime and terrorism cases.
"That communications data is information on the time, duration and dialling numbers of a phone call, it is not the content of that phone call and that is an important distinction.
"What we do need to make sure is that as technology changes we are able to maintain our current capability in this area."