The Bucharest Nine (B9) group of former Warsaw Pact countries was formed in 2015 and holds regular meetings of the leaders, foreign and defense ministers of its members: Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, and Slovakia.

However, a spokesperson for the Latvian president told Reuters that Budapest would be represented at Tuesday’s summit by its ambassador to Latvia rather than by President Tamás Sulyok.

At recent meetings, Hungary has obstructed resolutions to increase military aid to Ukraine and to accelerate the country’s accession to NATO. Budapest has also hampered EU efforts to assist Kyiv and to bring it into the bloc.

Ahead of the B9 summit in Riga on Tuesday, people close to the talks told the Financial Times that Hungary was once again planning to stymie a draft statement already agreed upon by the other members. The sources told the paper that discussions on excluding Hungary were “very serious,” with one insider telling the FT, “we are likely to be meeting in this format for the last time.” Another source described previous talks as “tough” and said it would be difficult to hold future sittings of the group under such circumstances.

Hungary’s nationalist prime minister, Viktor Orbán, said in May that his country sought to “redefine” its NATO membership due to his opposition to arming Kyiv.

“Our lawyers and officers are working [to define] how Hungary can exist as a NATO member without taking part in NATO operations outside NATO territory,” he told national radio.

Despite the apparent dispute, the Lithuanian president’s office said Hungary was invited to take part in Tuesday’s summit.

“Hungary is invited to the B9 summit in Riga on the 11th of June,” the office said. “It is important to keep Hungary in for the unity of NATO and the EU.”