Austria opposed expanding the passport-free Schengen zone to Romania and Bulgaria at a meeting of European Union interior ministers a year ago, saying illegal immigration was still too high and that the two countries needed to do more to prevent it before joining.

After they agreed tighter border security measures and won backing from other EU states, Austria has partially relented, proposing entry in stages, a solution Austrian Interior Minister Gerhard Karner referred to as “Air Schengen.”

Romania and Bulgaria are on major routes for illegal arms trade and drug and human trafficking, but the European Commission has said a thorough investigation has shown they met all Schengen requirements.

Romania has said Austrian opposition was unjustified, citing EU border agency Frontex data showing illegal migrants were mainly entering the EU from the Western Balkans, not Romania.

Austria’s ruling conservative People’s Party has for years made fighting illegal immigration a key campaign issue. The far-right Freedom Party, which has a similar line on migration, leads in opinion polls ahead of parliamentary election due next year.

Romanian Prime Minister Marcel Ciolacu welcomed the partial entry agreement.

“From March, Romanians will benefit of Schengen advantages on air and sea routes,” he said. “I am convinced that in 2024 we will finish negotiations for land borders as well.”

Joining Europe’s open-borders area would add half a percentage point to Romania’s annual economic growth, the finance ministry has estimated.