Polish President Aleksander Kwasniewski warned that Warsaw could veto a proposed new European Union constitution if Poland's voting powers were downgraded.
Referring to the draft constitution to be debated by EU leaders at a Brussels summit this weekend, Kwasniewski told BBC television: "If the position is what is in the treaty, without the chance for compromise, we cannot say yes.
"At the end of the day we are right," said Kwasniewski, adding: "We are right to fight for good equilibrium in the European Union."
The president was speaking ahead of a crucial European Union summit starting Friday, where leaders will aim to finalise the 15-nation bloc's first constitution as it prepares for its biggest enlargement yet, with 10 more countries including Poland due to join on May 1.
Warsaw, along with Madrid, is set to insist on hanging on to voting rights it gained in the EU's 2000 Nice Treaty.
That treaty gave Spain and Poland 27 votes, compared to 29 for Germany, whose population is bigger than that of the two countries combined.
Poland and Spain are fighting off efforts in the EU draft constitution to correct the imbalance, while France and Germany insist on keeping the draft in its current form.
Polish Foreign Minister Wlodzimierz Cimoszewicz said earlier Wednesday that the EU summit could fail but it would not be fair to blame Warsaw.
"We cannot, alas, rule out a fiasco ... because the extremely polarised positions are expressed in a radical way," Cimoszewicz said in an interview with Polish public radio Trojka.
"If people do not agree there will simply be no agreement," he said.
"As regards the voting system (in the EU's decision-making Council of Ministers), there is no big problem, because we have the Nice system. It has the force of law and will remain in force," he said.
Cimoszewicz also accused France and Germany of not respecting rules of "fair play" by blaming Poland and Spain for the impasse.
