BRUSSELS (Reuters) - The European Union’s executive will sue Poland, Hungary and the Czech Republic in the bloc’s top court for their refusal to host asylum-seekers, two EU sources said on Wednesday.

The European Commission will announce the decision on Thursday, the sources said, stepping up a legal case it opened against the three last summer.

The countries have declined to shelter asylum-seekers despite an overall drop in arrivals due to tighter borders and projects beyond the EU’s frontiers to discourage migration to Europe.

They say the mainly-Muslim refugees have no place in their homogeneous, predominantly Christian societies and cite security concerns given deadly attacks by Islamist militants in Europe.

Their reluctance to help host migrants from Africa and the Middle East who came to Europe mainly in 2015 has opened a rift with many other European governments.

These include Greece and Italy, two countries that have been the first port of call for refugees and migrants, as well as Germany and other wealthy Western nations that are frequently their preferred final destinations.

They say the post-communist countries have failed to show sufficient solidarity with their peers and have threatened retribution, including siphoning away some of the funds the bloc contributes to their development.

The eastern states have already lost one case on the matter at the Luxembourg-based European Court of Justice. The new case heralds months of legal wrangling on an issue that has undermined the EU’s ability to tackle other problems.

The dispute has also blocked reform of the bloc’s broader asylum system, which collapsed under the 2015 influx as governments struggled to control the situation.

The number of new arrivals has fallen sharply since then. This has made finding a policy solution less pressing. EU states aim to arrive at a compromise by mid-2018, though it is unclear how a deal will emerge.

The EU’s 28 interior ministers meeting in Brussels on Thursday will not even look in detail at the latest asylum proposal, which is by Estonia, diplomats and officials said.