The European Commission said in a statement that it has repeatedly urged the three countries to relocate refugees or at least pledge to do so under the legally-binding refugee plan agreed two years ago.

But it said they haven't taken action "in breach of their legal obligations," and that it "has decided to launch infringement procedures."

The plan to share 160,000 refugees in overwhelmed Italy and Greece among other European countries over two years was endorsed in September 2015 by a qualified majority vote.

But just three months before the September 2017 deadline, fewer than 21,000 people have been relocated.

The Czech Republic, Hungary, Romania and Slovakia voted against it. Hungary and Slovakia had previously launched their own legal action against the scheme.

EU Migration Commissioner Dimitris Avramopoulos said the Czech Republic, Hungary and Poland have until Wednesday to change their minds.

"There is still time ahead. Let's hope that not only reason but also the European spirit will prevail," Avramopoulos told reporters, lamenting that the three "have not done anything for more than one year."

But Poland said it stands ready to take legal action of its own.

"Poland is ready to defend its standpoint before the Court of Justice," Deputy Foreign Minister Konrad Szymanski said Tuesday.

He warned that the commission's action "may deepen the divisions within the EU."

Avramopoulos praised Austria and Slovakia for recently pledging to do more. But as of June 9, Austria had still not relocated a single refugee. Slovakia had taken in 16.

The refugee scheme was seen as a major plank of the EU's migration policy, and was lauded as a pan-European show of solidarity in 2015 when more than a million people arrived in Europe seeking sanctuary or jobs.

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