Poland's ruling nationalist Law and Justice (PiS) party on Monday nominated three new judges, two of them former hardline PiS lawmakers, to the Constitutional Tribunal, a move its opponents said further weakened judicial independence.

The European Union and human rights groups have long criticised PiS for tightening its grip over the courts as well as over state media and state companies.

PiS, whose mix of conservative nationalism and generous social spending helped it win a fresh four-year term in last month's parliamentary election, says its judicial overhaul was needed to improve the efficiency of the courts and root out the vestigal traces of communism in Poland, which fell 30 years ago.

Ten of the tribunal's 15 judges are already PiS appointees. The new nominees must be approved by the lower house of parliament, the Sejm, where PiS has a majority.

One of the nominees is former PiS lawmaker Stanisław Piotrowicz, who as a state prosecutor in communist times was known for prosecuting an opposition activist in the 1980s and for halting a case of sexual harassment of a minor by a priest.

The second nominee, also a former PiS lawmaker, Krystyna Pawłowicz, is known for her harsh attacks on the opposition and activists. In a tweet on Saturday she suggested that green activists and defenders of gay rights were serving "evil".

The third candidate for the constitutional tribunal, academic Elżbieta Chojna-Duch, is a former deputy finance minister. Last year she said Lech Wałęsa, a Nobel peace prize laureate and hero of the anti-communist Solidarity movement, had harmed Poland while serving as its president in the 1990s.

Responding to the nominations, Marcin Kierwiński, a lawmaker from Poland's largest opposition party, the centrist Civic Platform, said: "This is the destruction of the Polish justice system".

"They (the nominees) are to turn off the light in the independent Constitutional Tribunal," Kierwiński added.

But PiS denied the nominations were based on political considerations.

"There is no mockery here, we are very serious about these candidates. This is not politicisation, we are proposing people who have the appropriate competences and relevant experience," PiS parliamentary caucus head Ryszard Terlecki said.

The tribunal rules on the constitutionality of acts of law.