Home Secretary Jack Straw was due to outline the proposal - which will allow police to seize cash and property of suspected criminals even before conviction - on Sunday.
" It shows the vacuum that there is at the centre of Jack Straw's policy thinking "
Tory chairman Michael Ancram
But the Conservatives - campaigning on tax and the government's handling of the foot-and-mouth crisis - moved quickly to dismiss the idea.
The Liberal Democrats, in the wake of riots in Oldham on Saturday night attacked Tory language on asylum for encouraging intolerant behaviour.
The accusation - from which Mr Straw distanced himself - was dismissed by Conservative leader William Hague.
Meanwhile, an NOP opinion poll, published in the Sunday Times, suggests no change in support for the three main parties since last week, with Labour on 49%, the Conservatives 30% and the Lib Dems 14%.
Under Labour's proposals for the seizure of criminal assets, police would only need to have reasonable grounds for believing money was gained from crime or about to be used in it.
Mr Straw will also say that bureaux de change, some of which have been used to launder criminals' money, should be regulated as they are in the rest of the EU.
And he will say Labour would aim to double the amount of assets to £50m a year by the end of the next parliament.
But the Tories have already accused Mr Straw of repeating previous announcements.
Tory party chairman Michael Ancram said: "This government is very good at producing rabbits out of hats but they are stale rabbits which have been produced many times over.
"It shows the vacuum that there is at the centre of Jack Straw's policy thinking."
Mr Hague, meeting people affected by foot-and-mouth in his Yorkshire constituency, accused Tony Blair of "turning his back on farmers" during the crisis.
Later shadow chancellor Michael Portillo, in Essex, was due to revive the party's attack on government "stealth taxes".
Labour hopes to douse claims it has kept senior figures away from real people, with an election broadcast on Sunday evening it says is "part of its determination for real dialogue with the public".
Tony Blair and other cabinet ministers are to field telephone calls direct from the public at the end of the broadcast, which is a personal profile of Mr Blair by young film maker Jack Price.
Liberal Democrat leader Charles Kennedy kept the euro debate running by saying a referendum on the issue in the next two years was "inescapable".
He was speaking after Mr Hague warned the "no" campaign would be likely to lose a referendum on whether to join the single currency.
Mr Kennedy told the BBC: "This boil has got to be lanced one way or another".
He also appealed to voters to support his party as the only one offering "intelligent opposition with integrity".
In the last 11 days of the campaign he predicted the electorate would realise the Conservatives were heading for "meltdown" and vote Lib Dem to counter another huge Labour majority.
Also on Sunday, the Green Party was due to stage a mock episode of the television show The Weakest Link to support its claim that it holds the best policies for the environment.
In Edinburgh, Scottish National Party leader John Swinney is billed to make a keynote speech on the need for strong representation at Westminster.
And in Cardiff, Labour Party defectors to Plaid Cymru will stage a protest at what they say are Tony Blair's plans to privatise parts of the NHS.