A secret deal struck between party leaders fast-tracking legislation to allow police and MI5 to access your mobile and internet data has been branded a "stitch up".
The new law will be "railroaded" through parliament next week, Labour MP Tom Watson said on Twitter, after it was announced this morning.
The law is essential to keep you safe, David Cameron has said.
The prime minister said "events in Iraq and Syria" - a reference to gains made by the Islamist terrorist group ISIS - showed now was not the time to "scale back" on surveillance.
It follows intense controversy over the government's powers to snoop on your communications, after the explosive revelations about how the US government snoops on the phones of Americans and foreign politicians, revealed by whistleblower Edward Snowden.
Cameron and his Lib Dem deputy Nick Clegg have struck a deal on the measures after the junior coalition party blocked previous plans for a "snooper's charter".
Coalition sources said the Labour leadership had been briefed last week and were thought to be supportive.
Watson said the emergency legislationwas denying MPs the chance to canvass voters' views and said he would vote against its parliamentary timetable and probably elements of the package itself.
"This is a secret deal between party leaders, there hasn't been a bill published, we find out this morning when Parliament is on a one-line whip and MPs are in their constituencies that next week they will railroad through emergency legislation," he told BBC Radio 4's Today programme.
"That doesn't seem right to me. There are hundreds of thousands of people out there very concerned about this particular policy issue. They have not seen this bill either.
"If you are an MP, you probably shouldn't bother turning up for work next week because what you think doesn't really matter.
"The way it is looking now, I probably will be voting against aspects of it. I will certainly be voting against the programme motion."
Lib Dems who strongly opposed the so-called 'snooper's charter', such as Julian Huppert, have been closely involved in designing the safeguards.
Labour MP Tom Watson said the bill was 'a stitch up between party leaders', including his own
Cameron said: "It is the first duty of government to protect our national security and to act quickly when that security is compromised. As events in Iraq and Syria demonstrate, now is not the time to be scaling back on our ability to keep our people safe.
"The ability to access information about communications and intercept the communications of dangerous individuals is essential to fight the threat from criminals and terrorists targeting the UK."
The government has been forced to act as a result of a European Court ofJustice ruling in April that a European Union data retention directive, which was implemented by Labour in 2009, was invalid because it interferes with the fundamental right to respect for private life.
Downing Street said the emergency Data Retention and Investigation Powers Bill would "enable agencies to maintain existing capabilities", bring in tougher oversight of monitoring, and include a "sunset" clause requiring it to be renewed after two years.
Cameron said there would be "grave" consequences if the government did not make the changes.
"I want to be very clear that we are not introducing new powers or capabilities - that is not for this parliament. This is about restoring two vital measures ensuring that our law enforcement and intelligence agencies maintain the right tools to keep us all safe," he said.
Theresa May, pictured arriving at this morning's cabinet meeting, will make a statement to parliament when the details are finalised
Clegg said: "We know the consequences of not acting are serious, but this urgency will not be used as an excuse for more powers, or for a 'snooper's charter'.
"I believe that successive governments have neglected civil liberties in the pursuit of greater security. We will be the first government in many decades to increase transparency and oversight, and make significant progress in defence of liberty.
"But liberty and security must go hand in hand. We can't enjoy our freedom if we're unable to keep ourselves safe."
The proposals were discussed at an emergency Cabinet meeting this morning, and will be fleshed out by Cameron and Clegg at a rare joint press conference. Home Secretary Theresa May will then make a statement to parliament.
Police and security services had raised fears that without a legal underpinning and business need to keep information, companies would start deleting communications data that is often crucial for investigations into a range of serious crime including terrorism, child pornography and drugs trafficking.
The Bill, which is just six clauses long, will mean firms can retain data for 12 months. It is expected to go before the Commons on Tuesday, and be passed by both Houses by the end of the week.
The government needs to access your phone data now more than ever, Cameron said
He continued: "The government were aware of this European Court of Justice ruling six weeks ago.
"They are ramping up the rhetoric on it but no one in civic society has a chance to form a view on this or lobby their MP or talk to them about it.
"It is a stitch-up. I understand that Labour's shadow cabinet is seeing it this morning. They've not had a chance to think about it yet."
Intelligence and Security Committee (ISC) chairman Sir Malcolm Rifkind - who said he was briefed on the proposals on Tuesday - said they were "broadly speaking...necessary" but the ISC would need to look at the detailed terms.
The Bill should simply "replicate what currently exists with the safeguards that are clearly needed and may not have been in the European directive", he said - noting that it was unusual to get such agreement between party leaders.
"If that is what they are doing, then that is something we can all be very comfortable with.
"If we are satisfied that that is what the bill does, then I think the public can be reassured."
The Tory former foreign secretary said it was "obviously sensible" for the party leaders to seek consensus in such an urgent situation and MPs would have every chance to vote on the measure, which would also have to be approved by the House of Lords.
The Lib Dems stressed the legislation avoided the pitfalls of the so-called "snooper's charter" plans. The number of bodies able to approach communications companies to obtain data will be restricted, with some losing their access rights altogether and councils having to go through a single central authority.
A full review of the Regulation of Investigatory Powers Act will be held in the period before the legislation needs to be renewed, and the current Independent Reviewer of Terrorism Legislation will be beefed up to create a US-style Civil Liberties Oversight Board to scrutinise new government policy.
There will be annual reports on the use of surveillance powers to ensure more transparency.
A senior diplomat will also be appointed to lead talks with the US and the internet companies on forging an international agreement on sharing data between legal jurisdictions.