Tony Blair is worried that the proposed merger of the Transport and General Workers', Amicus and GMB would give the 2.6 million-strong new union too much clout at the conference, where the unions and constituency parties each have 50 per cent of the votes.
The proposed union and Unison would between them control more than a third of the total conference votes.
Informal talks between the party and the unions will discuss whether the three existing unions should keep separate block votes after the merger. Another option is to allow all unions to split their votes to reflect the balance of opinion among their members.
Blairites are worried that the image of union bosses wielding such huge block votes could damage the party in the run-up to the next election. Some want the unions' 50 per cent share of the conference votes to be cut to allow party members more influence in the hope this would attract more members.
Stephen Byers, the former cabinet minister, told a fringe meeting staged by the modernisers' group Progress: "Whether we like it or not, the whole question of the role that the trade unions play in party policy-making has to be considered. We need to value party members as an asset, not regard them as an institution to be tolerated."
Yesterday Mr Blair told the unions to "get real" after a conference in which they defeated the party leadership on secondary industrial action, pensions and health. The conference backed by 71 per cent to 29 per cent a Unison motion calling for a halt to the NHS using the private sector to carry out operations. But constituency parties opposed the move by a margin of 58 per cent to 42 per cent.
The Prime Minister told Sky News that in the past, the constituency delegates were seen as "the crazy ones" at Labour conference and the unions the force for stability but suggested the roles were now reversed. "The trade union movement has got to modernise, it has got to understand that the world out there has changed," he said. "I think this is the message from the constituency delegates to them: 'C'mon guys, get into the modern world, get real.'
"If they carry on in that position, it won't make a difference to Labour Party policy, but it will start to make a difference to how people regard the trade union movement."
Alan Johnson, the Trade and Industry Secretary and former leader of the Communication Workers' Union, said the electoral college which chooses the Labour leader was no longer sustainable and should be replaced with a "one member, one vote" system.
He told a Young Fabians' fringe meeting the proposed super union would place too much power in too few hands. The new merged union would wield about 22 per cent of the votes in the electoral college.
Mr Johnson argued that Trotskyists, Tories, Liberal Democrats and independents who were union members and paid the political levy should not be allowed a say in who leads Labour.
The new super union alone would command around 28 per cent of the votes at the Labour conference and 56 per cent at the Trades Union Congress.
A merger between the Transport and General Workers' Union, Amicus and the GMB has been discussed for months by senior officials, who are acutely aware of the power such a super-union could wield. The 2.6m membership would constitute a giant cross-industry union, with a potential £200m in assets. Amicus has a membership that spans the manufacturing, defence, tobacco and food and drink industries.
The T&G represents privatised bus drivers, farmworkers , dockers and car workers, while the GMB represents low-paid workers in the hotel, clothing and local government sectors, along with the NHS. Union leaders believe a unified organisation would be better placed to resist New Labour attempts to introduce further market models in the public sector.Reuse content