Britain's sixth-biggest union has voted to fund anti-austerity candidates in parliamentary elections where it thinks the Labour candidate is not sufficiently opposed to spending cuts.
The 292,000-strong Public and Commercial Services Union (PCS), which is not linked to Labour, is the first major union to have a policy of backing candidates who stand against the party. A spokesman denied that the union is trying to found a rival political party.
The union, which represents middle and low-ranking civil servants, announced this weekend that its members had voted four to one in favour of using union funds to back anti-austerity candidates.
This means union-backed candidates could stand against sitting Labour MPs who are perceived to have supported the coalition's cuts.
Although Labour has often faced competition from independents or fringe party members from the left, some of whom have been prominent trade union activists, these candidates have never been able to dip into union political funds to cover the costs of their campaigns.
The decision by the PCS marks a new stage in the union's long-running battle against public spending cuts, which has included strikes and a publicity campaign. The union has never had a formal link to the Labour party. Its general secretary, Mark Serwotka, was a member of a small revolutionary Marxist group when he was young, and has voted for the Green Party.
Union officials insist this is not the launch of a political party to compete with Labour. They hope the threat will induce constituency Labour parties to choose what a union spokesman called "genuine Labour candidates" who will oppose public sector cuts.
However, a Labour candidate in a by-election or the general election who says some cuts are necessary could now face an opponent backed by the country's sixth biggest union.
"It will be in exceptional circumstances rather than a general principle," a union spokesman said yesterday. "We're not starting a new party, but if there is a constituency where there has been the closure of a government office or cuts to the NHS and the main opposition parties are not opposing these cuts, we might considers supporting our own candidates or collaborating with others."
The change was backed by 78 per cent of those who took part in the ballot, conducted by post and online. But a low turnout of about 20 per cent meant the move was actually endorsed by about one member in six.