BRUSSELS/WARSAW (Reuters) - The European Commission took another step on Wednesday in its unprecedented investigation into the rule of law in Poland, saying it would send its criticisms to Warsaw by Monday unless it saw “significant progress” by then.

Poland said it would need more time, though it added that the two sides had narrowed some of their differences.

The EU executive launched its inquiry into whether the rule of law is under threat in Poland after the nationalist-minded government sought changes in the constitutional court that critics said undermined democratic checks and balances.

This has led to an effective paralysis of the tribunal, which has become the focus of heated political dispute.

The Commission has not disclosed the contents of the text, or ‘opinion’, it plans to send to Warsaw but it has expressed concern over conflicts around the appointment of judges to the tribunal and over new disputed laws amending the court’s work that have undermined its ability to review new legislation.

“As long as Poland’s Constitutional Tribunal is prevented from fully ensuring an effective constitutional review, there can be no effective scrutiny of compliance with fundamental rights of legislative acts,” the Commission said in a statement.

The Commission said Warsaw would have two weeks from Monday to respond to the ‘opinion’ and then should work with Brussels to remedy problems it has identified. If that does not happen in a “reasonable time”, the Commission can set Warsaw a formal deadline to deliver.

Deputy Foreign Minister Konrad Szymanski said Poland needed more time.

“The consultation process (between Poland and the Commission) has been going on for many weeks. I am under the impression that it has brought about a meaningful bridging of the gap between our positions,” Szymanski told reporters.

“But we certainly need more time ... For example legislative changes require parliamentary work, so it seems Monday should be seen as an auxiliary date, not an ultimatum for sure.”

Since the Commission launched its probe, the ruling Law and Justice party (PiS) has agreed to reverse some but not all of the changes affecting the court. The opposition has branded the PiS move as “political theatre”.

STRAINING TIES

If Poland fails to resolve the constitutional deadlock, Brussels could move towards the maximum sanction of stripping Warsaw of its voting rights in the European Council, which groups EU governments. This is seen as unlikely.

Some EU countries, already annoyed with Poland over its refusal to show greater solidarity in tackling Europe’s migration crisis, have threatened to use a looming review of the EU’s joint budget to siphon some funds away from the bloc’s largest eastern state.

Others, however, say Brussels should avoid a spat with Poland at a time when the migration crisis is testing EU unity and fuelling Euro-scepticism across the continent.

The Euro-sceptic government in Warsaw has so far offered few concessions to Brussels, saying it has a strong electoral mandate to carry out changes it deems necessary. It also says the top court had been too closely allied with the former centrist, pro-EU government.