Mr Lech Walesa, Poland's former president and one-time leader of the ground-breaking Solidarity union, called on Ireland to shoulder its "historic responsibility" and back EU enlargement at a weekend referendum on the Nice Treaty.
Mr Walesa, also a Nobel peace prize winner, said in a statement quoted by PAP news agency an Irish vote in favour of the treaty would represent an act of "European solidarity and an historic act of responsibility on the part of the Irish people."
Mr Walesa said the treaty was not perfect, but "it is always possible to improve on it."
"The most important thing is the spirit of the treaty which refers to stability and peace on our continent, without walls dividing it, without glaring inequalities, with perspectives of development for all the people, including those in my country who have gone through a lot in the course of their history."
He said that the continent's integration, "however difficult, was the only answer to war and inequality".
Solidarity, created by Walesa in 1980 as the first free trade union in the former Soviet bloc, succeeded in overthrowing Poland's Communist regime.
AFP