BRUSSELS (Reuters) - An adviser to Europe’s top court said on Thursday that a supreme court reform in Poland could undermine the independence of its judiciary, adding pressure on the Warsaw government to row back on changes that EU authorities say threaten the rule of law.

Since taking office in 2015, Poland’s eurosceptic Law and Justice (PiS) party has taken a series of steps that the European Commission says have increased government control over the courts.

The advocate general to the European Court of Justice said on Thursday that a newly-created Supreme Court disciplinary chamber “does not satisfy the requirements of judicial independence under EU law”.

Changes modifying the way in which judges are appointed cast doubts on its independence, Evgeni Tanchev said in a statement.

In a separate case on Monday, the ECJ ruled that Poland’s lowering of the retirement age for supreme court judges was against EU law.

The disciplinary chamber is composed solely of judges selected by the National Council for the Judiciary, whose members have been appointed by the PiS majority in parliament.

As part of the judicial overhaul, judges could be subjected to a disciplinary investigation and ultimately sanctions if authorities deemed their rulings inappropriate.

The ECJ, which is due to issue a final ruling in the coming months, is not bound by such opinions but follows its adviser’s lead in most cases.

In Warsaw, the government said it disagreed with Tanchev’s opinion.

“We believe that all regulations concerning the (Polish) judiciary... meet international standards. In a lot of countries the mechanisms function in a very similar way,” a spokesman said.

The PiS has so far paid little heed to criticisms emanating from Brussels, where the EU executive has struggled to find an effective response to what many in western Europe see as creeping authoritarianism in the eastern wing of the bloc, notably in Hungary and Romania as well as Poland.