Lew Adams, leader of the rail union Aslef, which is involved in the series of one-day strikes on the London Underground, also accused Mr Blair of reneging on promises to make British Rail publicly owned and publicly accountable.
Mr Adams will be seen as a voice from "Old Labour" and he attacked "stupid politicians", including the Prime Minister, on GMTV for calling him a dinosaur and Aslef headquarters Jurassic Park.
But his remarks highlighted the view among party traditionalists that the modernisers have to be checked in their zeal to ditch "Old Labour" baggage.
"At the moment we hear people say that Labour has got 100,000 new members. Well some of those are fair-weather friends that are here while the 'in' word is to be a member of the Labour Party.
"But the Labour Party was there to represent the workers, in industry, within transport and all other spheres of life."
His warning came with renewed reports that Mr Blair is planning to distance Labour further from the unions after the election. There were weekend reports that he will opt for state funding of parties, ending the union sponsorship which the Conservatives have claimed has made the unions the paymasters of Mr Blair's New Labour.
Senior colleagues will be alarmed by any move by Mr Blair to weaken unions ties further. The Labour leader has given private assurances to some colleagues, including John Prescott, the deputy leader, that there will be no divorce between the party and the unions.
The leadership has repeatedly denied that it is seeking to end the links with the unions, but that has failed to stop suspicions being raised among the union leaders.
A survey in the Sunday Times yesterday of 100 senior trade unionists showed that one-third believed Mr Blair would sever Labour links with the unions after the election, and one-third said they were ready to withhold payments to the party because they were losing influence.
Mr Adams also said Labour was moving away from its commitment to ensure that Railtrack was publicly owned and publicly accountable, and he said it was "sad" to see the demotion of Clare Short, the former transport spokesperson.
"Let's be honest with people instead of trying to get votes on a populist theme. Bash the trade unions - a few extra votes, I don't think so."
Glenda Jackson, promoted in the shadow ministerial reshuffle by Mr Blair to become number two to Andew Smith on transport, published a dossier accusing the Tories of 10 lies about rail privatisation.
Ms Jackson said the "lies" included John Major's assurance that privatisation of British Rail would ensure passengers got a better deal. The managers at the Porterbrook train-leasing company had scooped pounds 80m last week in the sale to Stagecoach.Reuse content