The European Union on Tuesday stepped up its legal threats to Poland over its controversial Supreme Court reforms, giving Warsaw one month to comply or risk being hauled before the bloc's top court.

The move raises the stakes in a bitter, long-running confrontation between the European Commission and Poland's right-wing government over the rule of law in the former communist state.

Brussels launched so-called infringement proceedings against Warsaw on July 2 over the changes introduced by the ruling Law and Justice party (PiS), which critics say put the judicial system under government control and are a threat to Polish democracy.

The European Commission said that after carrying out a "thorough analysis" of Warsaw's response, it had now decided to begin the second step of legal action against Poland.

"The response of the Polish authorities does not alleviate the Commission's legal concerns," it said in a statement.

"The Polish authorities now have one month to take the necessary measures to comply with this Reasoned Opinion. If the Polish authorities do not take appropriate measures, the Commission may decide to refer the case to the Court of Justice of the EU."