Serious delays in implementing a European Union plan to combat illegal immigration has jeopardized Greece’s membership of the bloc’s Schengen area, reports said on Friday.

Foreign officials, including members of the European Commission in Brussels, have made unannounced visits to the country in recent days to evaluate Greece’s progress in meeting its commitments.

Dutch Immigration Minister Gerd Leers on Wednesday also toured a reception center for immigrants in the northern Evros region for a firsthand evaluation.

“We have come to see the region where many migrants arrive and witness the way they are being received,” he said.

EU interior ministers meeting in Luxembourg last week reportedly criticized Athens after a large number of illegal migrants from Afghanistan and Pakistan were recently arrested in Serbia and Hungary after making their way through Greece.

Although Greece’s status among Schengen countries has not changed, officials say, “our peers never miss an opportunity to criticize our delays in designating areas for the new reception centers.”

Citizens’ Protection Minister Christos Papoutsis on Tuesday said that Greece, under fire for failing to prepare an action plan on illegal immigration, may have to leave the 25-member Schengen zone, which allows passport-free travel in the area.

Drawn up in May, the blueprint foresaw 14 sites being made available to accommodate migrants.

Despite some progress in assessing asylum applications, Greece is still lagging in the designation of areas where new reception centers will be built, as well as in upgrading existing facilities.

Authorities have reportedly stepped up efforts to build a new center in Filakio, Evros. The plan is to accommodate migrants in prefabricated houses, at a cost of 844,000 euros.

The European Commission has said that border controls can be reintroduced to deal with unexpected migration flows or if a Schengen country fails to monitor its borders with non-EU countries.