By Steve Schifferes
BBC News economics reporter at the TUC in Brighton
When the Conservatives under Mrs Thatcher ran Britain, the trade union movement seemed to embrace the European Union as an alternative to Thatcherism.
Many union leaders see the EU as a vehicle for privatization
EU president Jacques Delors famously appeared at the TUC Congress to rapturous applause.
There he extolled the virtues of 'social Europe' where workers rights were enshrined in international law and social benefits were provided on a Europe-wide basis.
This vision of a social Europe lived on for a number of years in the trade union movement, even as the EU proceeded in the 1990s to introduce the single currency and proceed with closer economic integration.
But now the British trade union movement seems united in its opposition to closer integration with Europe.
The campaign to force the government to hold a referendum on the new European Treaty is gathering widespread support among major unions, which might back it in a vote on Wednesday.
And this could prove one of the biggest headaches for Gordon Brown who has inherited Mr Blair's policy of a pro-European but pro-business stance with a firm desire to avoid a vote he might lose.
What has changed among the unions, and why?
According to John Monks, the president of the European TUC, and a former general secretary of the TUC, the government has only itself to blame.
He told the BBC that their "carelessness" in neglecting the social issues in Europe - in order to appease UK employers - may now rebound on them.
Mr Monks argues that it was wrong of the government to promise the CBI when it opted in to the social chapter in 1998 that it would block future social legislation - an agreement it has honoured with the exception of the directive on worker consultation.
And surprisingly, one of Mr Blair's key advisors on Europe, Roger Liddle, who now works for the European Commission, agrees.
He told a fringe meeting that it is now vital for Europe's future legitimacy that it embraces social issues as well as market liberalization, and he was wrong to advise the government on its pro-business stance a decade ago.
But it may be too late to win back trade union support for this position even though Gordon Brown apparently promised to make progress on a key issue - whether temporary workers employed by agencies should have the same rights as others.
Times have changed since Jacques Delors addressed the TUC
While an earlier generation of trade unionists may have been prepared to give the government the benefit of the doubt on this issue, the newer generation of more left-wing leaders sees Europe as leading the way to privatizing jobs and liberalizing markets.
Scepticism about the new liberal European agenda has grown.
From the very beginning, public sector unions like Unison worried that strict rules on government spending put in place by Europe could block Britain from investing in public services and running a budget deficit.
Now other leaders like Tony Woodley and Derek Simpson of Unite - the merged T&G and Amicus Union - and Paul Kenny of the GMB, are much more reluctant to endorse European integration on its present terms, and less trusting of Labour's intentions in this area.
And as the debate on the European constitution has shown, the public across the EU has also grown more sceptical of the concentration of political power in unelected hands.
Some unions are concerned that the UK opt-out from the fundamental bill of rights in the new treaty means that trade unionists in Britain will have fewer rights than those on the continent.
Paul Kenny says that the government has broken its word to have a referendum, and that it had explicitly pledged to do so in the Warwick agreement with the trade unions before the last election.
His union is leading the calls for a referendum.
Mr Kenny says he is not anti-European, but he believes that as long as unions are getting so little from Europe, opposition will grow. Mr Kenny even believes that the £2m his union contributes each year to the Labour party could be in jeopardy from angry members.
Mr Monks thinks it would be a disaster for the European cause if the unions in the UK force a referendum that would have repercussions across the continent, and deprive many workers of additional rights.
But his views may be out of touch with the current mood in the TUC.
For many years it was the Conservative party that was convulsed by divisions over Europe.
The collapse of the new Labour consensus on Europe and increasing battles within the Labour movement could be a serious development for Mr Brown as he contemplates his electoral options.