Supporters of closer European integration have accused larger member states of hijacking the forum drafting an EU constitution to boost their own powers at the expense of the wider European interest.
The Convention on the Future of Europe is trying to complete the draft in time for a summit of EU leaders in Greece on June 20-21, but divisions remain deep over how to distribute power in a Union due to expand from 15 to 25 members next year.
"We get the impression we are constantly tilting at windmills," said Elmar Brok, a senior member of the European Parliament and of the 105-member Convention, which is due to debate the latest draft text later this week.
"This is not acceptable to small member states. Do we want a directorate in Europe where the big six states decide everything? If so, it will be the end of the European Union," the German Christian Democrat told a news conference.
He accused the steering presidium headed by former French President Valery Giscard d'Estaing of riding roughshod over the views of the majority of the 105 Convention members, and of the majority of smaller EU member states.
The presidium proposes creating a long-term president of the European Council, the supreme EU body grouping national leaders. At present, the EU presidency rotates among all member states, irrespective of size, every six months.
The "big six" - Germany, Britain, France, Italy, Spain and Poland - back the reform, saying it will bring greater focus.
The draft would also cap the size of the European Commission, the EU executive which upholds the supranational EU interest, at 15 full members.
This is anathema to most small states, which insist on having their own Commission members in Brussels.
Brok said the proposals would reduce the Commission to "a machine for making the single market run" and the European Parliament to a rubber stamp while real power would lie with the national governments in the Council.