Poland's opposition parties and rights activists are due to stage a protest in the capital Warsaw against the government's reform of the judiciary.
They say the bill, passed by the Senate on Saturday, will erode judges' independence and undermine democracy.
The bill gives MPs and the justice minister the power to appoint judges without consulting judicial circles.
The government says the move is needed because the judiciary is corrupt and serve only the interests of the elites.
The bill must still be signed by President Andrzej Duda in order to become law. He has given no indication that he plans to veto it.
Since it came to power in 2015, the government of the conservative, populist Law and Justice party (PiS), has passed a series of controversial reforms, triggering mass protests.
Polish senators backed the judicial reform bill in a vote on Saturday morning after a heated debate.
Earlier this week, Justice Minister Zbigniew Ziobro had argued that the changes were necessary because the current system of appointing judges was undemocratic.
"We want to end corporatism and introduce the oxygen of democracy there. Because Poland is a democracy based on the rule of law.
"This is not court-ocracy," the minister said.
Many Poles agree with the government, the BBC's Adam Easton in Warsaw reports, but many others say this is not about reform but about political control.
Opposition parties are concerned that the law would give parliament – dominated by PiS lawmakers – an indirect control over judicial appointments, violating the constitutional separation of powers.
A separate bill was also presented in parliament this week, which would allow the justice minister to get rid of all of Poland's Supreme Court judges and appoint new ones.
This piece of legislation was not consulted on beforehand and introduced to parliament in the middle of the night, our correspondent says. It is still being discussed.
Under the PiS government, he adds, the justice minister already wields considerable power over the prosecution service in his role as prosecutor general because he can influence prosecutors to launch investigations.
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Grzegorz Schetyna, who leads the opposition Civic Platform party, denounced the tabling of the bill as an "announcement of a coup", the AFP news agency reports.
Earlier this week, the Council of Europe's Human Rights Commissioner, Nils Muiznieks, said the reforms were "a major setback for judicial independence".
Meanwhile, Manfred Weber, leader of the European Parliament's largest grouping the EPP, said: "Law and Justice is putting an end to the rule of law and leaving the European community of values."