A British Euro MP has been threatened with expulsion from the EPP group of MEPs after likening new powers with those given to Hitler in 1933.
Mr Hannan said he did not want to be rude to Mr Poettering
The European Parliament's German president Hans-Gert Poettering has been given extra powers to curb disruptions after protests by Eurosceptic MEPs.
Daniel Hannan said only his personal respect for Mr Poettering stopped him comparing the powers to a Nazi-era law.
Later he said he had not compared Mr Poettering to a Nazi, but apologised.
The Conservative Party is in the process of leaving the EPP, which it considers too federalist, and is attempting to form a new centre right group in Brussels and Strasbourg, although some of its MEPs have opposed the move.
The row was sparked by a point of order made by Conservative MEP Mr Hannan in the European Parliament chamber, as MEPs voted to give more power to Mr Poettering.
Mr Hannan complained about the stifling of free expression and likened the issue to the Germany's 1933 Ermächtigungsgesetz Act that gave Adolf Hitler unlimited power.
If MEPs backed the move, Mr Hannan said they would be abandoning their own rules.
He added: "I would almost be tempted to compare it to the Ermächtigungsgesetz law of 1933 but I think that would be disproportionate and perhaps a little rude to our president, who is a committed democrat and a decent man."
Writing about the row on his Daily Telegraph blog, Mr Hannan said: "As I sat down, the EPP leader, Joseph Daul, sprang to his feet and announced that he wanted me thrown out of the group.
"He had lost patience with my filibustering, he said. Enough was enough."
Mr Daul later told Mr Hannan he did not want the Tory MEP calling for an EU treaty referendum as a member of the EPP, the MEP writes.
But he said the Tory chief whip in Brussels backed his stance on a referendum and reassured him that he would continue to take the Tory whip and be re-selected as a candidate.
He said the row showed the Tories need an "amicable divorce" from the EPP.
A Conservative spokesman told the BBC that Mr Daul would make a decision on whether to expel Mr Hannan from the EPP when the Parliament next meets in Strasbourg.
Writing in his blog last week, Mr Hannan said he had been outraged by Mr Poettering's decision to suspend the European Parliament "in order to disadvantage the tiny number of MEPs who want a referendum".
But on Thursday he said: "I do not compare anyone to Nazis. I would certainly make no such comparison with Hans-Gert Poettering who, as I have always acknowledged, has an honourable record of opposition to totalitarianism, and who tragically lost his own father in the war.
"I am sorry if I hurt his feelings."
UKIP leader Nigel Farage praised Mr Hannan for his "bravery in working with UKIP and others in exposing the actions and anti-democratic nature of the European Parliament".
But Gary Titley, leader of the British Labour MEPs, said: "By comparing the ruling of the President of the European Parliament with the law that gave unlimited power to Hitler, in Holocaust week, Hannan is dishonouring memories of the victims of terror of the Nazi regime."
Graham Watson, leader of the multinational Liberal and Democrat (ALDE) group, accused Mr Hannan of "plumbing new depths in UK-EU relations and in the Tories' approach to democracy in the EU."
He added: "I trust that David Cameron will waste no time in dissociating himself from such an offensive remark."
Mr Poettering, a 61-year-old Christian Democrat who is also a former leader of the EPP group, was elected president of the European Parliament in January 2007.