A group of legal academics has sent a letter to parliament criticising the government for a "false" representation of its emergency snooping bill.
The group claims the bill will significantly extend the powers available to police and spooks, and include some powers that are "the first of their kind globally".
"DRIP [data retention and investigatory powers bill] is far more than an administrative necessity; it is a serious expansion of the British surveillance state," the academics said.
"We urge the British government not to fast track this legislation and instead apply full and proper parliamentary scrutiny to ensure Parliamentarians are not mislead as to what powers this bill truly contains."
The bill will give government snoopers the ability to compel those outside the UK to comply with government snooping, even if the activity under scrutiny occurs outside of British jurisdiction.
"DRIP attempts to extend the territorial reach of the British interception powers, expanding the UK's ability to mandate the interception of communications content across the globe," the academics added.
Labour said last week that they would support the bill, which is being put before the House of Lords today and is likely to pass into law before the summer recess.
Prime minister David Cameron previously defended the bill as a necessary response to a European Court of Justice judgement restricting companies' capacity to retain communications data.
However the academics contend that the bill "arguably breaches EU law", and strays from a previous EU privacy directive.
Contacted for comment about the letter, the government has yet to respond.