Northwestern European countries are discussing proposals for a smaller free-travel area inside the European Union, the Netherlands’ leading daily reports.

According to De Telegraaf newspaper, Belgium is keen on a Dutch proposal to exclude Central and Southern European nations from the Schengen Area while the Germans are skeptical.

Other remaining countries would be Austria and Luxembourg.

26 European countries have abolished border controls. The system is being called into question now that hundreds of thousands of migrants from Africa and the Middle East travel freely through border states like Greece, Hungary, Italy and Slovenia to the wealthier nations of Western Europe.

Friday’s terrorist attacks in Paris cast further doubt on the union’s open borders. At least one of the attackers was able to travel to Europe on a fake Syrian passport while others drove into Paris from Belgium.

France closed its borders after the attacks while Poland said it would no longer admit any refugees.

Germany earlier warned that Schengen could be at risk if Central European nations refused to take in more immigrants.

The country — Europe’s largest economy — expects to process as many as one million asylum applications this year. It has repeatedly called for a proportionate distribution of migrants across the 28 member states of the European Union but countries in the east, including Hungary and Poland, have refused.

Hungary built a fence on its border with Serbia to keep migrants out. Austria has similarly fenced off its border with Slovenia.

Germany is at the same time cautious about reversing what it sees as progress in the continent’s unification.

Europe’s open borders are also a boon to its export economy.

They are for the Netherlands too. Indeed, exports account for some 70 percent of the Dutch economy. But its two biggest trading partners are Belgium and Germany whereas the Germans trade more with Austria, France and Poland.

Halbe Zijlstra, the parliamentary leader of the Netherlands’ ruling liberals, said his party backed a redesign of Schengen. “The influx is so high, we need to take unorthodox measures,” he said on Wednesday.

Dismantling Schengen would involve more than reinstating border checks. The agreement, named after the Luxembourgish town where it was signed in 1985, also covers data sharing and a common visa policy.