An emergency European Union plan to help Italy and Greece manage thousands of migrants crossing the Mediterranean could be vastly watered down next week, diplomats said Friday.

The EU's executive commission wants EU interior ministers meeting next Tuesday to endorse its scheme to share responsibility for taking in 40,000 Syrians and Eritreans arriving in Italy and Greece. The plan would require EU countries to take in set numbers of refugees based on criteria like economic strength, unemployment and efforts already undertaken to host migrants.

But diplomats said that about 10 of the 28 EU nations insist the system should be voluntary, not mandatory. Hungary and the Czech Republic oppose the plan outright.

Even the states supporting it want to change the terms for sharing the refugees.

One EU diplomat said there's clearly not a majority needed to approve the plan. He declined to be named because he is not permitted to speak publicly about the deliberations.

Around 100,000 migrants have already arrived in Europe this year, many of whom crossed the Mediterranean Sea to reach Italy and Greece. Some 2,000 are missing and feared dead, and five countries alone are handling about three quarters of those who survived.

Given the frequent failure of EU nations to show genuine solidarity with front-line countries Italy, Greece and Malta, the commission had hoped that its plan would force them to share the burden.

The plan has become more urgent as migrants often arrive in greater numbers between June and September.

"We will defend our proposals to the last word," commission spokesman Margaritis Schinas said Friday.

But one seasoned diplomat suggested that the compromise the ministers could agree to might not be to the commission's liking.

"We will have to avoid the word 'voluntary' and the word 'mandatory' and then find a way for everyone to participate," he said.

EU leaders will discuss the plan at their summit in Brussels on June 25-26. If no agreement is reached by the next interior ministers' meeting in July, the plan could be put on hold until September.

The European Trade Union Confederation, which has long supported the migrantcause amid what it believes is a humanitarian crisis unfolding in the Mediterranean, expressed dismay at the lack of support.

"It is outrageous that the proposals ... have now been met with a backlash using arguments that sound irresponsible and often xenophobic," a statement said.