Lech Walesa, the former Polish president and leader of the opposition to communist rule, joined protests against plans to put the judicial system under the ruling party’s political control.
The 73-year-old Walesa on July 22 told a crowd in the northern city of Gdansk to use "all means" to protect their democracy.
"Our generation succeeded in putting Poland back on track and ensuring the separation of powers," he said, referring to Poland's transition to democracy in the 1980s. "We cannot allow anyone to destroy that."
Protests in cities throughout the country have mounted since Poland's Senate on July 22 defied the European Union and approved legislation giving political leaders substantial control over the court system.
The legislation calls for firing current Supreme Court judges, except those approved by the president, and it gives the president power to regulate the courts.
EU leaders have criticized the bill for impairing judicial independence and threatening the rule of law.
The bill sponsored by the nation's populist ruling party now only needs the signature of President Andrzej Duda within 21 days to become law. Duda has adhered to the ruling party line up to now.
On July 22, presidential spokesman Krzysztof Lapinski said Duda sees some flaws in the legislation, but he did not say whether the president would reject the bill or seek the opinion of the Constitutional Tribunal.
Thousands of protesters gathered in Warsaw, Krakow, and other cities to urge Duda to reject the legislation.
Many of the protesters in the capital marched to the Supreme Court, where people held candles and sang the John Lennon song Imagine.
Jaroslaw Kaczynski, head of the ruling Law and Justice party, argues that the judiciary still functions as it did during the communist era and harbors many judges from that time. Communist rule ended in 1989.