European leaders on Thursday, Feb 12, said they would use the region’s law-enforcement databases more extensively to prevent citizens from traveling overseas to fight with terrorist groups in Syria and elsewhere, the Wall Street Journal reports.

The change is part of the European Union’s response to the growing ranks of its citizens who have left to fight in Syria’s civil war, mostly with Islamic State. Those “foreign fighters” have challenged the bloc’s commitment to allowing free movement of people across the Schengen zone—a region of 26 European countries where passport and customs checks at national borders have been abolished.

“We agree to proceed without delay to systematic and coordinated checks on individuals enjoying the right of free movement against databases relevant to the fight against terrorism based on common risk indicators,” the leaders said in a statement.

The principal database in question is the Schengen Information System, which contains arrest warrants, travel alerts and other information pooled from national police forces across the Schengen area, the Journal says. For example, the database would allow authorities at Frankfurt airport to know that the French police have placed a travel alert on a French resident who is flying to Istanbul, a common waypoint for European fighters headed to Syria.

The Schengen rules, however, prevent national authorities from checking every European citizen crossing a Schengen border against the database. Most governments want to change the rules to allow universal checks, officials say, but such a move would require approval of the European Parliament.

The European Commission, the EU’s executive arm, which has the sole right to propose European legislation, is wary that starting such a debate could open up Schengen to changes that would restrict free movement, at a time when some politicians have been seeking to limit migration within the Schengen area.