The newly-elected President of the European Parliament, Mr Pat Cox, has said he would not feel constrained by his new office from campaigning for the Nice Treaty in a second referendum.
He would be doing so as a citizen and MEP, rather than as a representative of the Parliament itself.
The Green MEP, Ms Patricia McKenna, said yesterday it was "an abuse of power".
Mr Cox told The Irish Times: "First of all, as a citizen in Ireland, I have a constitutional right of freedom of association and freedom of expression.
"Secondly, as a public representative, I have a right, a responsibility and a duty to be engaged.
Thirdly, I have been engaged in every European campaign since we started.
"I think the constraint has to be that I cannot, when I give my own view to the Irish electorate as an Irish representative, suggest or pretend that this is the view of this institution [European Parliament], which clearly it is not, and this institution is not entitled to tell the Irish electorate how to behave.
"The second thing; any staff on assignment to the office of President of the Parliament would not be misused in any way . . . as part of such a campaign."
When asked if he would also campaign for adoption of the euro if invited to do so in a British referendum, he replied: "The delicacy would be rather different in its style and tone because I don't have a mandate from the people in other states quite in the way that I am entitled to exercise it in Ireland."
Ms McKenna, an MEP for Dublin, said Mr Cox's stance was the reason she could not support him in the election for the presidency even though he was an Irish candidate.
"It is an abuse of power," she said.
It was unreasonable of Mr Cox to ask people to distinguish between himself and his new role.
"You cannot separate the fact that you are President of the Parliament and go home and say: 'You are not to look at me now as President of the Parliament, you are just to see me as an individual, Mr Pat Cox, MEP for Munster'," Ms Mckenna said.
The Green MEP for Leinster, Ms Nuala Ahern, said Mr Cox had "a perfect right" to campaign in a second Nice poll provided he did not use the resources of the Parliament in an inappropriate manner.
"He says he is going to campaign as a European citizen and as somebody [who is] elected and has a mandate, and he has a perfect right to do that as far as I am concerned.
"I would be watching carefully that he doesn't use the resources of the Parliament to campaign in a national referendum in Ireland inappropriately, and I think, therefore, Patricia is right to watch that."
However, Ms Ahern favoured negotiating a new treaty rather than holding a second referendum.
"We're being asked to answer the same thing twice and I think the Irish people will vote against that."
The Fine Gael MEP for Dublin, Ms Mary Banotti, has been re-elected at the head of the poll for the office of Quaestor, or MEPs' representative, in the European Parliament.