A summit is being held in North Macedonia on developing a so-called mini Schengen zone in the Western Balkans.
Serbia, North Macedonia and Albania, want a single market that would allow the free movement of people, goods and services.
So far, the trio have agreed to impose single work permits and allow easier border crossings between them.
Leaders from Montenegro and Bosnia and Herzegovina will attend Wednesday's summit but it's unclear if they are ready to sign up to the initiative.
It comes as momentum for joining the European Union grinds to a halt.
Serbia, Albania, North Macedonia and Montenegro all applied to join more than a decade ago, but they have still not been accepted into the bloc.
This project, called the Open Balkan initiative, has the support of Washington and Brussels, with EU commissioner Olivér Várhelyi due to travel to the summit.
“I welcome the renewed impetus by leaders in the Western Balkans to advance on regional integration," said Várhelyi.
"The war Russia has waged in Europe is a wakeup call on the need to speed up the EU accession process, a geostrategic investment in the stability and security of the whole of Europe.
"Inclusive regional cooperation, based on EU rules, is key to bringing the Western Balkans closer to the EU's single market, which is at the heart of our shared prosperity."