The European Commission will decide next month on any legal cases against countries failing to host migrants as agreed in a 2015 deal.
European Union's 2015 decision to settle migrants across Europe has proven controversial and fewer than 18,500 people have been relocated so far under the two-year plan meant to cover 160,000 people.
While some EU states have been slow and taking migrants in reluctantly, countries like Poland and Hungary have refused to host a single person. The two countries have now been given a June deadline to start admitting their share of migrants from overstretched Italy and Greece or risk sanctions.
"I call on Poland and Hungary who have not relocated a single person ... to start doing so right now," EU Migration Commissioner Dimitris Avramopoulos told reporters in Strasbourg, France.
"If no action is taken by them before [our)] next report in June, the Commission will not hesitate to make use of its powers under the treaties and to open infringement procedures," he said.
But Poland and several other countries remain defiant.
"I am not afraid of these thundering pronouncements by the Commission," Polish Prime Minister Beata Szydlo said.
"We will not agree to the imposition on Poland or any other EU country obligatory quotas."
TRT World's Sarah Morice has more.