WARSAW (Reuters) - Thousands of anti-government protesters marched in Warsaw on Saturday demanding “independent” courts following a judiciary overhaul which has sparked a row with the European Union.

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The conservative and euroskeptic Law and Justice party (PiS) came to power in 2015 on promises of delivering large social benefits to Poles.

However, the government has come under severe criticism at home and abroad for taking control over key institutions such as the constitutional court and the public media, and by doing so angering the EU.

Saturday’s “Freedom March”, organized by opposition parties, saw several thousands of protesters gather in the center of Warsaw, many of them carrying European Union flags.

It comes at a time when leadership of Nowoczesna party, a smaller partner of the main opposition the Civic Platform Party (PO), has fallen apart, weakening the entire opposition block ahead of the local election in autumn this year.

“We will be fighting for freedom, dignity, democracy and for a Poland in Europe,” PO leader Grzegorz Schetyna said during a televised speech at the march.

Opposition accuses PiS of undermining democratic values, mostly by adopting laws which critics say threaten the independence of courts. PiS has argued the changes were necessary to remove judges left over from the Communist era.

The judiciary overhaul prompted the EU to trigger in December Article 7 of the Lisbon Treaty for the first time - a punitive measure which could lead to a suspension of Poland’s voting rights in the trading bloc.

Keen to end the Article 7 procedure, Warsaw has already offered some concessions and a compromise may be agreed at some point soon.

PiS has also upset many Poles with attempts to tighten the abortion law.

“They will not take the free courts from us, they will not deprive us from the freedom of choice, conscience and opinion,” said Katarzyna Lubnauer, the head of Nowoczesna.

Despite the criticisms, a recent poll by Pollster has revealed a 43 percent support for PiS, with a 20 percent backing for PO and 6 percent for Nowoczesna. In April, the opposition overtook PiS in opinion polls, largely due to contested financial rewards for ministers which had been approved by PiS.