The government will be able to transfer some powers from Britain to the EU without a referendum under new proposals, despite promising the public would get to vote on any such move.
The new EU Bill says a minister will be able to simply state the transfer of power is not significant enough to merit a referendum in some cases.
Ministers will then be able to make the change by passing an act of parliament.
The measure is likely to be fiercely opposed by Conservative eurosceptics.
Under the terms of the bill, published on Thursday, ministers will only be able to avoid a referendum by saying a change is insignificant where EU institutions are given powers to impose fresh obligations or sanctions on the UK.
Broader changes will have to be put to a public vote.
The minister's ruling could be challenged in the courts, and the government says it has no plans to transfer sovereignty or powers to the EU in this parliament.
The measure is likely to cause alarm among Conservative eurosceptics, who will point to the commitment in the coalition agreement to subject any future transfers of power to a "referendum lock".
The Conservative chairman of the European Scrutiny Committee Bill Cash has opened an inquiry.
Mr Cash said: "This bill is of historic significance and is the most important constitutional bill affecting the relationship between the UK parliament and the EU since the European Communities Act 1972."
Last November in a speech on Europe made while leader of the opposition David Cameron said: "Never again should it be possible for a British government to transfer power to the EU without the say of the British people."
MPs will get an opportunity to raise their concerns when the bill has its second reading in the House of Commons.
Introducing the bill, the Europe minister David Lidington said many British people felt "disconnected" from how the EU had developed and from decisions taken in their name.
"That is why we are introducing this EU Bill, to give people more control over decisions made by the government in the EU in their name," he said.
The legislation requires changes to EU treaties that move power or responsibility for policy from the UK to the EU, not covered by the significance exception, to be put to a national referendum.
The government has already made clear there will not be a referendum on treaty changes suggested by the German Chancellor Angela Merkel, to establish a permanent mechanism to protect the euro, because the UK says that would only affect countries which use the single currency.
That treaty change, the details of which have yet to be settled, will be subject to an Act of Parliament.
Labour said the bill was a "sop" to Conservative eurosceptics rather than a serious policy.
"Holding referenda on major constitutional and economic changes is the right thing to do," said shadow Europe minister Wayne David. "But this bill is a dog's dinner which could lead to costly wrangling in the courts over what it means, and whether we need referenda on tiny changes too."
And a member of the Liberal Democrat group in the European Parliament said the UK must work constructively with EU partners or risk "relegating itself to some uninfluential off-shore destination".
"The move to referenda seems to be calculated to appeal to a populist and nationalist constituency which undoubtedly exists in the UK," Andrew Duff said.
"The coalition government must respect the constitutional order of the European Union and should not impede the steady democratic evolution of the Treaty-based rules which bind all EU states together in a deep and lasting interdependence."
The legislation is also likely to give the Conservatives another member of the European Parliament as it ratifies an earlier agreement that will lead to an extra MEP's seat in the West Midlands.
The returning officer will use the last European election results to identify the candidate who most narrowly missed out on a seat. That would lead to a new Tory member, who could take his or her place as early as 2011.
The legislation also includes a clause declaring EU law only takes effect in the UK because the parliament in this country allows it.
The sovereignty clause writes into statute something already established in common law. A measure of this sort was promised in both the Conservative election manifesto and the coalition agreement.