BRUSSELS—European countries won’t decide on plans to redistribute migrants before September, several European Union officials said Monday, a further setback in the bloc’s response to the migration crisis in the Mediterranean.

The European Commission, the EU’s executive arm, last month presented a set of plans, including a binding quota system aimed at relocating the 40,000 Syrians and Eritreans—expected to arrive in Italy and Greece over the next two years—to 23 other EU countries. The commission was hoping that home affairs ministers would hold a vote on the plan next week to help the two countries who are facing a steady stream of migrants crossing the Mediterranean from Libya. Last weekend alone, 5,700 migrants arrived on the Italian coast and the trend is likely to increase over the summer.

But the plan has been kicked into the long grass, with ministers planning a “discussion” for next week and awaiting further guidance from EU leaders who will meet in Brussels on June 25-26.

“At next week’s justice and home affairs council, ministers will discuss the European Agenda on Migration. We don’t expect a decision,” said Janis Berzins, spokesman of the Latvian EU rotating presidency organizing the ministers’ meetings.

A commission spokeswoman said, “We will wait for the discussion with the ministers in the council and it will also be on the agenda of the European Council at the end of June.”

In April, days after 800 migrants capsized on their way to Italy, EU leaders held a snap meeting deciding to increase their naval presence in the Mediterranean, set up a military mission to fight people traffickers and to look at ways to help refugees and countries under migratory pressure. The commission then went a step further with the redistribution mechanism for the 40,000 Syrians and Eritreans expected to arrive in Italy and Greece.

The plan was immediately criticized by eastern member states—Poland, the Czech Republic, Hungary and the Baltic states—who resent any binding quotas. They argue that they lack the capacity and their societies lack the experience with refugees that more affluent states have. Poland is pointing to the 300,000 visas it issued to Ukrainians last year in a gesture of “solidarity” with people escaping a war zone.

A majority of larger member states—led by Germany who is in favor of the redistribution system—could force the mechanism into life, “but it would create a serious backlash in the eastern countries,” said one EU official.

In addition, France and Spain have voiced criticism at how the quotas are calculated. The countries claim they don’t sufficiently take into account past efforts to accept refugees or to invest in fending off illegal migration—for instance in Spain’s enclaves in northern Africa.

Meanwhile, the EU military mission in the Mediterranean to fight traffickers and sink their boats is also being delayed, in the absence of United Nations’ approval.

The only concrete measure implemented so far is the increase in assets and the surveillance area of the EU’s border patrol mission, Triton, now carrying out most rescue missions in the Mediterranean. But migration-wary countries, notably the U.K., are fearing a pull-factor; that is, attracting even more migrants because they can be certain of rescue. One way to counter that, and keep their support, is to shift the debate toward an increase in the return of migrants denied asylum, says another EU official. Currently, only 40% of the return decisions are enforced, according to EU statistics.