The unions last year accepted a rule change that allows their voting strength at the policy-making conference to fall below half the total. But they did so as part of a private understanding with the Labour leader that this would not happen. "Tony gave us his word that we would keep half the votes," said a union insider yesterday.
The Left-wing Campaign for Labour Party Democracy believes that Mr Blair and his fellow-modernisers may be about to renege on the deal.
CLPD has circulated a model resolution, certain to be taken up by some unions and constituency parties, which seeks to commit the conference against "all proposals that would further weaken ... the voting strength of affiliated organisations."
It adds: "The Labour Party needs the trade unions and the unions need the Labour Party. Our party came into being to represent the interests of its affiliated levy-payers. Without the link to the unions, Labour would degenerate into a rootless SDP-Mark II."
The idea of drawing a line under curbs of union power is also attracting support among members of the Campaign Group of MPs. Ken Livingstone, MP for Brent East, said: "There is no question of any further weakening of the trade union link. Both Labour MPs and the unions are totally opposed to that.
A spokesman for the Labour leader denied that any further diminution in the trade union vote was envisaged. But he added: "Tony Blair has never said there will never be any further change."Reuse content