He also said the Socialists, the second biggest faction in the EU assembly, would vote against the centre-right Portuguese politician if the issue is put on the parliament's agenda during its mid-July session.

Daniel Cohn-Bendit, leader of the Greens, accused member states of "steam-rolling tactics" over the issue.

The July meeting is the parliament's constitutive session after the June European elections and both groups are arguing that there will not be enough time to properly consider Mr Barroso's re-appointment.

"The Council's wish to run this past a meeting of the European Parliament leaders at the end of June, followed by a vote in July, rather than to have a full and official consultation of the parliament, is wholly unacceptable," said Mr Schulz.

However, both groups still fall far short of a majority in the 736-strong parliament. Mr Cohn-Bendit claims that Liberals and the far left will also support him in his wish to postpone the vote.

Member states are hoping that consultations beginning next week will be enough to find a compromise on Mr Barroso's renomination.

He is supported by the largest group in the parliament, the centre-right EPP. Socialists and Greens dislike him for what they see as his pro-free-market policies and are hoping that new candidates will be in the running come September.

Under a vote in July, Mr Barroso would need to get a simple majority of those present in the chamber to secure his nomination.

The negotiations next week are expected to shed some light on whether it will be possible to get the green light from the parliament.

The Socialists say that appointing him now would cause legal uncertainty, as a new treaty – the Lisbon Treaty -might then be in place.

This would mean that the rest of the commissioners would be appointed under a different set of institutional rules.

However, diplomats have suggested that Mr Barroso would simply be commission "president-designate" until the entire commission is voted on in the autumn, and then his presidency would be signed and sealed.

In addition, there is also a suggestion that Mr Barroso should try and aim for an absolute majority in the parliament (369 votes) in the July vote.

In this way he would have fulfilled the voting requirement of the Lisbon Treaty, should final ratification in the remaining countries be completed later this year.