By Pawel Sobczak and Gabriela Baczynska
WARSAW (Reuters) - Three Polish opposition parties boycotted a special session of parliament on Friday to mark the centennial of independence, in protest against changes by the ruling Law and Justice (PiS) party they see as undermining democracy.
Since taking office in late 2015, PiS has been accused by the European Union, rights groups and the domestic political opposition of undermining the rule of law. The EU has launched an unprecedented punitive procedure against the largest ex-communist state in the bloc.
This year marks the 100th anniversary of Poland's independence, regained at the end of World War One from the collapse of the German, Austrian and Russian empires.
The government marked the event with a joint session of both houses of parliament. But the centrist opposition Civic Platform (PO) party and smaller opposition Nowoczesna party declined to attend and held a separate ceremony.
"The parliament became a machine to push through what the government needs," said Kamila Gasiuk-Pihowicz of Nowoczesna.
A third opposition group, the Polish People's Party (PSL), attended the beginning of the official event but walked out before the address by President Andrzej Duda, a PiS ally. PSL head Wladyslaw Kosiniak-Kamysz said the ruling party had turned the parliament into a mere "re-enactment group."
Addressing the gathering, Duda defended PiS policies.
"One cannot deny the parliamentary majority the right to implement its programme," Duda said.
The nationalist PiS has put pressure on critical media and non-governmental groups promoting liberal social values, as well as placing the judiciary under more direct government control.
PiS, which has 235 seats in the 460-strong lower chamber and 63 in the 100-strong upper chamber, denies accusations that its moves go against democratic standards. It says its measures are needed to improve the efficiency of courts and rid them of a lingering communist legacy.
Despite street protests and mounting international pressure, PiS has not budged and enjoys strong public support, in part due to more generous social spending.
"Judges are today much more independent than they used to be," Prime Minister Mateusz Morawiecki told the European Parliament earlier this month. "Democracy in Poland has never been as vibrant as is now. Citizens can exercise their rights with no obstacles. Media are more diverse."
(Additional reporting by Pawel Florkiewicz, Krzysztof Kruk and Anna Koper; Writing by Gabriela Baczynska; Editing by Peter Graff)