Members of the convention on the future of Europe have been criticising proposals from their chairman, Valery Giscard d'Estaing, to alter the EU's power structures.
Giscard has a hard fight ahead
Mr Giscard d'Estaing wants a full-time EU president to represent the Union internationally and to chair meetings of the council of EU leaders.
He has also suggested cutting the number of commissioners from 20 to 15.
"You have not listened to us, or you would have taken our concerns into account," German representative Johannes Voggenbauer said at the beginning of Thursday's meeting of the 105-member body.
"For a year now we have been working hard. Your proposals throw our compromises to the wind," he said.
Former Irish Prime Minister John Bruton suggested Mr Giscard d'Estaing's draft would be rejected.
"It does not have wide support here," he said.
However, after amendments made to the proposals on Wednesday, the European Commission said it had fewer objections.
'Battle for power'
Chief Commission spokesman Reijo Kempinnen said the draft was a "useful working basis".
Chaired by Valery Giscard d'Estaing
Holding year-long discussions
Aims to simplify treaties
Trying to decide balance of power between Brussels and governments
While he added that the Commission would fight the idea of a full-time president "to the end", an un-named Commission official quoted by the Reuters news agency said the idea might be acceptable - provided the role of the Commission itself was strengthened.
On Wednesday, the Commission said that the bureaucracy surrounding the new president of the council would sow confusion and lead to competition with the European Commission and its president.
Correspondents say the Commission sees a risk that national governments will increase their power at its expense.
The BBC's Chris Morris says the debate in the convention over these latest proposals represents a battle for power in the EU as it prepares to expand from 15 to 25 members in 2004.
Mr Giscard d'Estaing has agreed to drop the idea of a vice-president and a co-ordinating bureau.
He also modified his original plan to cut the size of the Commission to 13.
Smaller nations' fears
Currently the council of EU leaders has a six-month rotating presidency.
The European Council shall elect its President, by qualified majority, for a term of 2.5 years, renewable once. The person elected must be, or have been for at least two years, a member of the European Council
There is widespread agreement that extra continuity would be desirable.
However, smaller countries fear that the larger countries would dominate the presidency, and that their influence would wane.
"We are trying to copy a President of the United States, a People's Congress of China and a Politburo of the Soviet Union," said Finnish representative Kimmo Kiljiunen.
At a European summit in Athens last week, 18 of the 25 current and future members of the EU rejected the idea of a permanent president.
But Mr Giscard d'Estaing pointed out that the larger countries, which supported the idea, represented a majority of EU citizens.
There is widespread agreement on Mr Giscard d'Estaing's proposal for a European Foreign Minister, who would sit on the European Commission and represent the EU abroad.
Another accepted as a basis for discussion is Mr Giscard d'Estaing's proposal for a People's Congress of national parliamentarians, to scrutinise EU policy, and possibly to choose the council president.
In less than two months the convention is due to present a draft constitutional treaty which will be taken up for discussion by EU leaders.
The idea is that it will replace all previous EU treaties with a single document, clearer and easier to understand.