Unison, the public sector workers' union, delivered a serious rebuff to the Labour leader by rejecting his proposals for updating Clause IV of the party's constitution, opting instead for retention of the commitment to public ownership.
And in a second blow to the leadership, John Monks, the general secretary of the TUC, led attacks on Mr Blair's plans for dealing with bad teachers as David Blunkett, the party's spokesman on education, came under fire from teachers' unions.
The day of setbacks for Mr Blair may mark the beginning of strains in the relationship between the Labour leader and the trade unions over the pace of modernisation. Mr Blair was accused of seeking "old Tory solutions" to the problem of bad teachers by Nigel de Gruchy, of the National Union of School Masters and Women Teachers.
The unrest was underlined by the Unison vote, in a conference hall in London where Mr Blair hopes in two weeks' time to win a majority to scrap the old Clause IV and replace it with a new form of words. "It shows you cannot take the trade unions for granted," said Geoff Martin, a leading opponent of change.
Mr Blair's office said Unison's members had been denied a ballot on the issue, and described yesterday's conference delegates as "unrepresentative". An official claimed that early returns from ballots of constituency party members were running at about 8 to 1 in favour of change.
Leadership sources said Mr Blair was still likely to win the vote on 29 April at the special conference. Although a number of unions have declared against the changes, some may vote both ways since new rules allow delegates to vote differently.
John Prescott, Labour's deputy leader, denied Mr Blair had misjudged opposition. "He knew it would be controversial ...The party are now, after the debate, going to give a decision. I am confident it will be along the lines he has recommended."
Labour's opponents took comfort from the rift. Unison's vote means the "honeymoon is over, the bubble has burst", said David Rendel, the Liberal Democrat spokesman on local government.
The harshest criticism from the unions came over Mr Blunkett's plans to give failing schools a "fresh start" by closing them down and reopening them with new staff, if necessary.
Mr Monks said: "I do not believe in adopting the style of a football team that changes the manager when things are going wrong. I hope that David Blunkett is not suggesting that the team gets changed just because the school is not doing well. Even Mr Chips, Jean Brodie and Socrates would not be able to change some schools. To put the blame on teachers is not right."
Peter Smith, leader of the Association of Teachers and Lecturers, told his union's conference in Harrogate: "Mr Blair's new model army - or at least its generals - seem to have judged that there are many Tory policies which, if adroitly repackaged, will bring them to power."
To round off a bad day for Mr Blair, Bill Morris, the transport workers' leader, criticised Labour for failing to promote its policy of a minimum wage more vigorously, and he embarrassed the leadership by calling for it to be set at £4 an hour.
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