By Wiktor Szary and Jakub Iglewski
WARSAW (Reuters) - Tens of thousands of Poles waving national flags staged a huge protest march through Warsaw on Saturday, accusing the conservative Law and Justice (PiS) party that took power last year of undermining democracy and putting Poland's European future at risk.
The throng stretched at least 3 km (2 miles) along a ceremonial boulevard leading past the presidential palace, and Warsaw Mayor Hanna Gronkiewicz-Waltz, a member of the opposition centrist Civic Platform (PO), put the number of demonstrators at 200,000.
Critics say the nationalist-minded administration is curbing democratic checks and balances and driving a wedge between Poland and its allies in the European Union, which it joined in 2004.
They also say the PiS's euroscepticism could push Poland, a former Soviet satellite, back into the Russian sphere of influence. PO leader Grzegorz Schetyna told the crowd it was the largest demonstration since Poland threw off communist rule in 1989.
Some PiS actions, including attempts to take more direct control of the judiciary and public media, have prompted the EU's executive Commission to launch a "Rule of Law" procedure, which could result in a suspension of Poland's voting rights.
The economically left-leaning PiS says it has to strengthen its hold over state institutions to share out the benefits of economic transformation more evenly, and that Poland needs to defend its interests more assertively in the EU.
While anti-government rallies are frequent, the PiS continues to enjoy strong popular support. A recent poll put it at 33 percent, only a few points down from October's election, and still well ahead of the largest opposition party in parliament, the PO.
Saturday's march was organized by various pro-European groupings and parliamentary opposition parties, including the PO and the liberal Modern (Nowoczesna) party, led by a former World Bank economist.
Waving Polish white-and-red and EU flags and chanting "we are and will be in Europe", the protesters demanded the PiS respect EU standards of governance.
"By not respecting European values, PiS is ensuring that we will first find ourselves on the fringes of the European Union, and then outside of it," Modern party spokeswoman Kamila Gasiuk-Pihowicz told the protesters.
"Only two trains leave from the historic station at which Poland is standing. One is the European Express. The other is the Trans-Siberian Railway."
The PiS released a video on Saturday in which party leader Jaroslaw Kaczynski, twin brother of late president Lech Kaczynski, said that "today, being in Europe means being in the EU".
"We want to be a member of the European Union, because we want to have an influence on Europe's fate. But our position depends above all on our strength. We have to gain a strong position, become a strong, European nation," Kaczynski said.
(Writing by Wiktor Szary; Editing by Kevin Liffey)