Austria, Belgium, Denmark France, Germany and Sweden have proposed to the European Commission to extend temporary controls at the internal borders of the Schengen Area to tackle migration flows more efficiently, Die Welt reported on Saturday.

The proposal has been made in a letter to the European Commission First Vice-President Frans Timmermans and Migration Commissioner Dimitris Avramopoulos.

The six countries called on the Commission to propose to the European Council to permit to maintain or introduce controls at internal Schengen borders from May 13 for a period of six months, if EU member states believe such move was necessary, according to the German newspaper.

Eight of the 26member states of the Schengen Area have introduced border checks since last September, including Austria and Germany, to stem the flow of migrants. Under current rules, such border checks can be introduced only temporarily and can’t be extended beyond May 12, unless the European Commission finds that EU’s free-travel areais at risk because of a country’s failure to protect the area’s external borders.

The closure of the Western Balkan migration route to Germany and Sweden and the start of sending back migrants and refugees from Greece to Turkey under a deal between the EU and Ankara reached in March have significantly reduced the number of migrants reaching central and western Europe. Yet, the number of migrants arriving in Greece and Italy by sea has increased in the first four months of 2016, compared to a year earlier, according to data from the International Organisation for Migration.

Concerned by prospects of resumed migration pressure at its borders, Austria re-introduced checks on its border with Hungary earlier this week and said it would impose border checks at the Brenner Pass on its frontier with Italy by the end of May.