Five of the world's largest website operators have warned Home Secretary Theresa May against implementing the controversial Communications Data Bill, which would allow law enforcement authorities to access data about web and email communications.
In a letter seen by The Guardian, Google, Facebook, Microsoft, Yahoo! and Twitter told May that the plan would be "expensive to implement and highly contentious".
They specifically oppose a proposed requirement for website operators from any country to store records of their UK customers for up to 12 months.
"We do not want there to be any doubt about the strength of our concerns in respect of the idea that the UK government would seek to impose an order on a company in respect of services which are offered by service providers outside the UK," the letter, which was sent in April, said.
The Communication Data Bill was vetoed by deputy prime minister Nick Clegg, but the murder of soldier in Woolwich last week has revived political support for the idea.
Speaking to the BBC in the wake of the attack, May reiterated her claim that the bill is needed to give police the data they need to tackle terrorism and the distribution of images of child sexual abuse.
“I have always been clear that access to communications data is essential for law enforcement agencies and the intelligence agencies,” she told The Andrew Marr Show. “There is a reducing capability in relation to access to communications data. The law enforcement agencies, the intelligence agencies need access to communications data and that is essential to them doing their job."
The web giants are the latest to voice their opposition to the bill. Also in April, a group of nine cyber security experts warned the government that the bill "combines high financial and privacy costs with low benefits for real police work".
"The money would be better spent on more police officers, on improving our police forces' computer forensic capabilities, and on international collaboration to tackle cyber crime, than on yet another IT project that already shows the classic symptoms of becoming a failure," they warned.