The new Polish Prime Minister, Donald Tusk, has told parliament that his government will refuse to sign the EU Charter of Fundamental Rights.
Donald Tusk says tells MPs he won't sign up to EU rights charter
Mr Tusk said the decision was out of respect for a deal negotiated by the previous conservative government.
But he promised to pursue a more pro-European Union policy, saying his government would ensure that "Poles and Poland are quickly ready for the euro".
Mr Tusk also confirmed Poland would pull its troops out of Iraq next year.
Poland currently has 900 soldiers serving in Iraq and the prime minister said the decision to pull them out had been taken because of its importance for Polish public opinion.
In campaigning for last month's election, his party, Civic Platform, had promised to bring the troops home.
"We are going to carry out this withdrawal in the knowledge that we have fulfilled - and even more than fulfilled - our commitments to our allies," he said.
In 2003, 2,600 Polish troops took part in the invasion of Iraq and led a force in the south-central area of the country.
The president, Lech Kaczynski, is commander of the armed forces and opposes withdrawal but does not have the power to challenge the government.
Before Mr Tusk's party came to power, the previous government led by the president's twin, Jaroslaw Kaczynski, announced that Poland would join Britain in opting out of the Charter of Fundamental Rights.
The document features in the EU Reform Treaty as no more than a short reference but Mr Kaczynski's coalition was concerned that some of the charter's provisions relating to moral and family issues could contradict Polish law.
There was particular concern about same-sex marriages which are legal in a number of EU member states.
The new government has no such objection and the prime minister told the Polish parliament that his party and its coalition ally, the Peasants' Party, were in favour of signing up to it.
But Mr Tusk told MPs that the opt-out would remain because he needed the support of Jaroslaw Kaczynski's party in order to reach the two-thirds majority required to ratify the Reform Treaty as a whole.
"Our European Union partners understand our situation," he said.
His three-hour speech in the Sejm (the lower house of parliament) is believed to be the longest ever given by a democratically-elected prime minister in Poland.