Plans to give the European Union power to set workers' rights in the UK will be blocked, the government has promised.
Valery Giscard d'Estaing's proposals will now be intensely debated
The proposals - which could mean a European judge having the final say on the right to strike - are the latest published in a draft text for a new EU constitution.
They would make an existing charter of rights legally-binding on EU states.
But a government spokesman said the plan can only be accepted if it does not add new legal rights beyond those currently applied in the UK.
The charter, introduced in 2000, is aimed at declaring basic freedoms but it reaches further on workers' rights and social policy.
Under proposals from the convention working on Europe's future, the charter would be given new legal force and would over-ride domestic law.
Most of the convention's draft text for the new constitution - including details of the charter - was unveiled on Monday.
More proposals were outlined on Tuesday, including plans to extend "qualified majority voting" (QMV) in EU-decision-making.
Under this system, votes are allocated to member states according to their populations, but are weighted in favour of smaller countries.
In some areas QMV could replace the system where all EU countries must agree on a decision.
The convention proposes that asylum policy be agreed by QMV, a plan backed by the government.
But ministers are opposed to another suggestion where immigration policy would be agreed by QMV.
The new proposals also include a "European Public Prosecutor" - opposed by the UK - with the right to operate in member states to pursue people suspected of "serious crime affecting several member states".
The plans envisage how the EU will be run after 10 new countries join
"This idea would mean setting up a whole new institution, which is the
reverse of what the convention is supposed to be doing," said the UK spokesman.
Another plan would increase the power of the European Parliament, more than doubling the number of
policy areas in which MEPs have equal say with EU ministers from 34 to 70.
The government has rejected Tory suggestions that UK sovereignty will be threatened, saying the final plans have yet to be agreed.
Wales Secretary Peter Hain, the UK government representative on the convention, said Britain had the power to veto any plans it opposes.
Chaired by Valery Giscard d'Estaing
Holding year-long discussions
Aims to simplify treaties
Trying to decide balance of power between Brussels and governments
He again rejected calls for a referendum on the plans, saying the government would ensure Parliament had ample opportunity to scrutinise the document "line by line".
If voters disliked the way the government had handled the issue they could express their views at the ballot box in next year's European elections, he said.
That comment prompted the Conservatives to ask whether Mr Hain was suggesting the European polls would be fought as a referendum on the convention.
Mr Hain said that was "absurd", while Downing Street said the Wales secretary was simply stating the obvious - that if people felt unhappy then they could make their views known at the ballot box.
Former chancellor Ken Clarke said the new constitution was a "great opportunity" to improve decision making in the EU.
He broke ranks with his party leadership, saying a referendum on the plans were unnecessary.
The draft proposals include calls for an elected EU president and foreign minister, and backing for a common foreign policy.
They are aimed at setting out a vision of how the EU will be run after 10 new countries join next year.
References to a "federal" Europe were dropped at Tony Blair's request. Calls to rename the EU as "United Europe" have also been rejected amid UK concern.
The 148 pages of proposals have been drawn up over 15 months by the 105 members of the convention, including government ministers, Euro MPs, MPs and the European Commission.
The draft will be debated by the convention this week and then considered by EU leaders at a summit in Greece in June.
A final agreement could take up to a year.