The Polish government's ability to send lower court judges to higher courts — and subsequently remove them without giving reasons — runs contrary to EU law, the European Court of Justice (ECJ) has ruled.
The Luxembourg court said there must be "guarantees to prevent any risk of those secondments being used as a means of exerting political control over the content of judicial decisions".
However, it found a number of factors that give the Polish justice minister the power to "influence those judges and may give rise to doubts concerning their independence".
In criminal cases, given that the Minister of Justice also occupies the position of Public Prosecutor General with power over the lower court and seconded judges, there may be "reasonable doubts... over the impartiality of those seconded judges", the ruling states.
It also questions the impartiality of seconded judges in disciplinary hearings.
Taken together, the ECJ says that the government minister's powers concerning seconded judges do not guarantee "the independence which all judges should normally enjoy in a State governed by the rule of law".
It adds that doubts over the impartiality of judges also calls into question the presumption of innocence in criminal cases.
The case arose after a Polish court asked the ECJ to determine whether the government's powers infringed the requirement for judicial independence.
Poland's nationalist government is involved in a series of disputes with the EU over judicial reforms and the rule of law, that critics say undermines the independence of the judiciary.