The ministers of NATO, a 28-member international military and political alliance, are scheduled to meet Tuesday and Wednesday in Brussels and will likely issue a unanimous invitation for Montenegro to join the group, the Guardian reported. If Montenegro joined, it would be the first new member since 2009 and would likely cause increased tensions with Russia, which has long seen NATO as encroaching on its sphere of influence in Eastern Europe.

“Montenegro has come a long way on its path to join the Euro-Atlantic family,” NATO Secretary General Jens Stoltenberg said Monday. “Extending an invitation to Montenegro to start accession talks would be a historic decision. It would signal our continued commitment to the Western Balkans.”

Russian President Vladimir Putin has described any expansion of the organization as a “provocation” to Moscow. Following Russia’s annexation of Crimea in March 2014 and the subsequent war in Eastern Ukraine, NATO has worked closely with its Eastern European partners, particularly in recent months.

“The countries in the periphery are now wondering what they can do to enhance their bilateral ties,” Julianne Smith, a senior fellow at the Center for a New American Security, a think tank in Washington, told International Business Times.

NATO and the U.S. have continued to deny that the group's potential growth is a response to Russian actions.

“This is not designed as a message to Russia; it is not about Russia,” Douglas Lute, the U.S. ambassador to NATO, said.

If the ministers meeting in Brussels decided to extend an offer of membership to Montenegro, a formal offer would take place at a NATO meeting in July in Warsaw, Poland. It would then take approximately 12 to 18 months for the full process to be completed. Montenegro’s Parliament has voted to join the alliance despite protests that some members claim have been fueled by Russia.

“Russian has been opposing NATO enlargement for years,” said Vesko Garcevic, Montenegro’s coordinator for NATO, the Wall Street Journal reported. “We would like Montenegro be part of NATO and the EU. This is where Montenegro should belong.”

Neighboring Albania and Croatia were the last two states to join the alliance in 2009. Bosnia and Herzegovina, Macedonia, Georgia and Ukraine have all also expressed interest in joining the alliance, further angering Russia.