The president of Poland’s supreme court has urged the country’s judges to “fight for every inch of justice” as the rightwing government pushes for changes that critics say would make judicial independence a “pure fiction”.

“For over a year I have been repeating that the courts are easily turned into a plaything in the hands of politicians,” Małgorzata Gersdorf told her colleagues in an open letter read out at a recent gathering of judges in Warsaw. “What was until now a threat is becoming a reality.”

In its latest battle with Poland’s legal system, the ruling Law and Justice party (PiS) says it wants to “democratise” the way Polish judges are appointed, which at the moment is a job for the National Council of the Judiciary (KRS), an autonomous body whose judicial members are chosen by their peers.

Under the government’s proposals, however, the terms of all the judicial members of the council would be terminated within 90 days of the draft law’s enactment. Their replacements would be selected by the Polish parliament, with the speaker of the parliament given discretion as to which candidates should be put forward for consideration.

Whereas the council’s judicial members presently enjoy a majority, under the government’s proposals the body would be split into two chambers, one for judicial members and the other for political representatives. Both chambers would have to agree to an appointment or a resolution, giving the political representatives a veto over decisions made by the judicial members.

“The government’s proposals will be an instrument for ensuring the appointment of the ‘right’ kind of judges who will not be too critical of the authorities and their political programme,” said Ewa Łętowska, a professor at Poland’s Institute of Legal Sciences and a former judge who served on the country’s constitutional tribunal and the supreme administrative court.

The council was given less than three working days to respond to the draft act, receiving it from the Ministry of Justice on a Thursday and expected to provide its official response by the following Tuesday. In a strongly worded statement, it described the proposals as “in obvious and gross contradiction with the Polish constitution”.

“The council is an independent constitutional organ that was instituted in 1989 in order to safeguard the independence of the judiciary, because in the communist era everything was dependent on the ruling party,” Dariusz Zawistowski, chairman of the KRS and a serving supreme court judge, told the Guardian.

“When members of the council are elected by the parliament, this function of safeguarding the constitution will be pure fiction. Formally speaking, there would be no independent judiciary.”

Gersdorf has urged her fellow judges to risk their own positions in the fight against the proposals.

“There is no fight without victims, and among them may be counted some of us present here,” said Gersdorf’s letter to her fellow judges. “To win, you must be prepared even for disciplinary tribunals, to be removed from office, for anything. You must show that we are in opposition to the pushing of a democratic state into oblivion.”

The government describes the proposals as “enhancing democracy and independence” by freeing the appointments process from “the corporate interests of the judicial environment”, citing the judicial appointments process in countries such as Spain and Germany.

“Objectivity in selecting members of the National Council of the Judiciary and their independence from corporate interests is to be ensured by them being selected by the Sejm, which holds a mandate gained in democratic elections. A similar system is successful for instance in Spain,” said the Ministry of Justice in a statement.

But the KRS’s response rejects such comparisons. “It must be recalled that in accordance with article 8(1) of the constitution, it is the constitution of the Republic of Poland of 2 April 1997 that is the supreme law in the Republic of Poland, and not the constitution of Spain of 31 October 1978 or the basic law of the Federal Republic of Germany of 23 May 1949.”

The controversy is the latest front in a protracted battle between the PiS and an increasingly demoralised judiciary.

Shortly after assuming power in late 2015, the government merged the office of prosecutor general with that of the justice minister, Zbigniew Ziobro, a move that some analysts argue has already allowed the government to exert political pressure on judges.

“We have already seen numerous examples of prosecutors answerable to the minister of justice initiating criminal proceedings against judges who have reached decisions they don’t agree with,” said Łętowska.