WARSAW — Thousands of government opponents gathered in Warsaw and other cities in Poland on Sunday to protest the latest changes in legislation that reorganized the judiciary.

The legislation that was adopted last week has drawn condemnation from European Union politicians and from Poland’s opposition. They say it violates judicial independence and the rule of law.

The protests, held under the slogan of ‘‘In the defense of the courts,’’ were the latest in a string of mass antigovernment demonstrations that have characterized the conservative, populist Law and Justice party’s 20 months in power.

Their main theme has been the defense of democracy under the ruling party, which controls both houses of Parliament. The fractured and weak opposition has posed little threat to the government, other than participating in the protests.

The noisy crowd in Warsaw was chanting ‘‘We will defend democracy’’ and slogans against the ruling party leader, Jaroslaw Kaczynski, who is Poland’s most powerful politician, whom they called a ‘‘dictator.’’

‘‘We, the citizens, are defending the rule of law; we are on the side of the law,’’ said one of the protest leaders, Wladyslaw Frasyniuk, a top prodemocracy activist in the 1980s.

The main opposition party’s leader and a former foreign minister, Grzegorz Schetyna, warned that the ruling party may use the new regulations to manipulate electoral returns.

Under the new legislation, lawmakers appoint members of the National Council of the Judiciary, which draws up and enforces ethical guidelines for judges, reviews judicial candidates, and seeks opinions on new rules and regulations to ensure they are constitutional.

Associated Press