Gordon Brown has rejected calls from two trade unions for the government to hold a referendum on the new EU treaty.
Critics say the treaty is the constitution by another name
The GMB and RMT had joined the Tories and UKIP in demanding a vote by tabling motions for the TUC annual conference.
They say the treaty is almost the same as the discarded EU constitution, on which a referendum was promised.
But the prime minister said: "The proper way to discuss this is through detailed discussion in the House of Commons and the House of Lords."
He added that he was confident Parliament would pass the treaty.
He told a press conference: "Let's see what the TUC do. My own view is that the TUC, when it meets, will support the government."
The RMT's motion asks the TUC to campaign for a "no" vote, if a referendum is held on whether to adopt the treaty.
Its general secretary, Bob Crow, told the BBC: "They [the government] went to the British people on the promise there would be a referendum."
He also said: "What we want him [Gordon Brown] to do is implement what his manifesto was."
The GMB union said it was concerned the UK's opt-out from the EU Charter of Fundamental Rights was being retained in the transition from the constitution to the treaty.
European officer Kathleen Walker-Shaw said the British government should opt back in to the charter before EU heads of state meet in October.
She added that the GMB had not yet decided how it would campaign in the event of the government calling a referendum.
But she went on to say it was unlikely the union would campaign for a treaty where workers would become second class citizens in Europe.
Ms Walker-Shaw said: "The government's position is not acceptable. We are giving them the chance to change it."
She added: "We want a social Europe. What sort of message is this preaching to developing countries that we are telling to raise working standards, when a government in Europe won't even accept them for its own people?"
Earlier this month, the Conservatives accused Mr Brown of trying to push the "unreadable" revised EU treaty through "on the quiet".
Shadow foreign secretary William Hague said: "By all the standards of the past, the commitment to a referendum should be upheld."
But the government says a referendum is not needed as the treaty is different to the constitution rejected by French and Dutch voters in 2005.
Gary Titley, Labour's leader in the European Parliament, said: "It's a world of difference between what was proposed in the constitutional treaty and the amending treaty."
He added that the EU was an ongoing "political process" which was designed to allow member states to "meet the challenges of globalisation".
UKIP, which campaigns for Britain to leave the EU, is also demanding a referendum on the treaty, calling on the government to "let the people decide".
Its leader, Nigel Farage, said it was "seriously good news" that unions were demanding a vote, adding: "Gordon Brown must be the only man in the country who doesn't realise that we have to have a referendum on this treaty.
"Every other political leader in the EU has said that this is the constitution in all but name, and the Labour Party was elected with a manifesto to hold a referendum on that document.
"He is doing a rather splendid impression of an ostrich, surrounding himself with yes men who are trying to drown out the overwhelming calls for the British people to have their say."