setting up a parliamentary clash that will be the first test of the prime minister's authority since the general election.
Members of the 30-strong socialist campaign group of backbenchers hope to halt the bill at its second reading next month amid concerns about the escalating cost of the ID card scheme and fears that personal information stored on a national register could be mis-used .
Their intervention is the first concrete sign that rebel MPs are prepared to make common cause with the opposition to exploit Mr Blair's new-found vulnerability.
With the Conservatives vowing this week to vote against the government the rebels could deprive Mr Blair of valuable support. In theory, only 34 Labour members would need to vote against the bill to halt its progress in the Commons.
Ministers, however, are desperate to avert a clash with the parliamentary Labour party so soon after the election. Charles Clarke, home secretary, held private talks this week with backbenchers known to be concerned, including the campaign group.
But he offered no concessions, and some MPs said on Friday that their concern had increased following an admission by the Home Office that the cost of the scheme had risen to £5.8bn. The government's original estimate, in 2002, was £3bn.
Kate Hoey, a former culture minister, said of the proposed scheme: "It's a complete waste of time and money and a fundamental change in the country I want to live in. I see no reason for it."