In a shock upset for Tony Blair, and a historic break from union commitment to the Labour party, delegates to the Fire Brigades Union (FBU) conference in Bridlington voted this morning to change the union's rules to allow financial support to candidates opposing the Labour party.

In future, the union will support only those candidates who back "the policies and principles of the union" - and in the debate it was made clear that that would not include the vast majority of Labour candidates.

The successful resolution was carried against the recommendation of the union's executive by a card vote of 27,000 to 23,000. It was moved by the FBU's London Region, and in the debate, a number of Socialist Alliance supporters spoke for the resolution.

"This historic vote is an expression of grass-roots disgust with New Labour's attacks on public services and trade unions," said Neil Thompson, the Socialist Alliance candidate against Shaun Woodward in St Helens South, following the result.

"Trades unionists are clearly looking for an alternative to New Labour and every day increasing numbers are coming out in support of the Socialist Alliance. It's not surprising. After all, unlike New Labour, the Socialist Alliance actually supports and campaigns for the policies of the trade union movement.

"It's high time UNISON members, in particular, asked themselves why their dues were being used to fund a New Labour campaign whose main election pledge is to privatise the services they work in and undermine their jobs and conditions."

Four fire-fighters and FBU activists (all delegates to the FBU conference) are standing as Socialist Alliance candidates in the general election: Joe Hearne (Luton South), Dick Duane (Basildon), Steve Godward (Birmingham Erdington) and Neil Thompson (St Helens South). Their candidacies are known to have played a major role in precipitating the FBU debate and in the result of the card vote.

Steve Godward, standing in Erdington against New Labour parachute job Sion Simon, said: "It's now down to individual candidates, not the New Labour Machine. We have firmly rejected the view that there's only one party to support. The Socialist Alliance proves it is a real alternative to the Big Three."

Joe Hearne, who has just won the Arthur Charles Memorial Prize with an essay about the Socialist Alliance, commented: "This was vote of no confidence against the Labour Party from a leading union. This clearly flags up the possibility of a break-up of the constitutional links with the Labour Party."

The list of trade union supporters currently posted on the Socialist Alliance website includes the senior elected officers (chairs or secretaries) of more than 130 trade union branches (including more than 30 UNISON branches), more than twenty trades councils, plus more than 200 public sector shop stewards or workplace reps.

In addition there is one current general secretary of a major national trade union, two past presidents of other major unions, and a number of current national executive members of trades unions (including RMT, UNISON, NUJ, Writers Guild).