The European Court of Justice (ECJ) will hold a hearing on Friday (1 June) on a case that could be a make or break the EU's efforts to uphold rule of law in the bloc.

The 17-member grand chamber in Luxembourg will hear arguments spelling out whether Poland's judiciary has been compromised after an Irish high court judge in March refused to extradite a suspected drugs offender to Poland due to concerns about the integrity of the Polish justice system.

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Justice Aileen Donnelly referred the case of Polish Artur Celmer, arrested on drugs charges in Ireland last year, to the ECJ because the recent changes in the Polish judicial system had been "so immense" that Ireland's high court had been forced to conclude that the rule of law in Poland had been "systematically damaged" and the "mutual trust" underpinning the European arrest warrant process had been compromised.

The European Commission, last December, launched the so-called Article 7 procedure against Poland.

The unprecedented sanctions process could see Poland punished for putting its judiciary under political control.

Dialogue between Brussels and the Polish government has been bumpy and the commission has given Warsaw until the end of June to comply with the EU executive's recommendations by rolling back some of the changes.

If it does not, fellow member states could decide to impose the sanctions the commission proposed.

The commission has been using the argument that safeguarding rule of law and the independence of the courts is crucial because a breach in one EU country has an effect on the union as a whole.

Courts are interdependent by upholding EU law in justice cooperation and internal market issues.

If the ECJ rules that Poland's judiciary has indeed been compromised, it would not only be a damning verdict on Warsaw's overhaul of the courts, it also could add fuel the commission's arguments.

However, the ECJ could also take a more narrow view and focus only on Celmer's case, without answering the broader question on the situation in Poland.

The Irish Times reported on Thursday (31 May) that Ireland will make the case that the Polish man would get a fair trail if deported to Poland and that the commission will back that argument.

"This is a make or break moment for the ECJ to play a decisive role in the Polish rule of law situation," Laurent Pech, professor of European law at Middlesex University told EUobserver, adding that it was very difficult to predict which route the court will take.

One of the worst scenarios for Warsaw would be that all European arrest warrants coming from Poland would be stopped and that other EU mechanisms based on "mutual trust" would halt as well.

If the ECJ's summer ruling tackles the wider concerns regarding Poland's judiciary, it "could reinforce the European Commission's negotiating power in the Article 7 discussions or could weaken it, if it says there is no issue in Poland," Pech added.

Meanwhile, Warsaw chose a combative approach.

Pro-government Polish media ran personal attacks on the Irish judge.

Mariusz Muszynski, vice-president of Poland's constitutional tribunal, whose appointment has been disputed accused the ECJ of political, pro-EU bias and of over-interpreting EU law.

"This 'guardian of the Treaties' violates the rule of law itself," he wrote.

The Polish government has already had run-ins with the EU's top court, as it hasignored a previous ECJ ruling to stop logging at the country's primeval Bialowieza forest.

Pech said the ruling comes at an important time, and could help prevent other countries backsliding on rule of law issues.

Hungary's nationalist government, which has a two-thirds majority in parliament, earlier in the week tabled a constitutional amendment calling for the establishment of so-called administrative courts that could pave the way for loyalist judges to rule on politically sensitive issues.

In Romania, the constitutional court, in a controversial ruling on Thursday, limited the president's powers and gave the justice minister, a political appointee, more control over prosecutors.

After Friday's hearing, the ECJ's advocate general will issue an opinion and the chamber is expected to rule before mid-July because the case has an "expedited" status as the Polish drugs suspect is currently in custody.