Greek Prime Minister Alexis Tsipras has said he will call a confidence vote after his governing coalition split over the Macedonia name change.
Defence Minister Panos Kammenos withdrew his party’s support, signalling his opposition ahead of an expected vote in the Greek parliament.
The two countries recently agreed that Greece’s northern neighbour would be called North Macedonia, therefore ending a 27-year-long row.
Macedonia has ratified the deal.
Greek nationalists argue that the name “Macedonia” can only refer to the Greek province of the same name.
The dispute, which has raged since it voted for independence from Yugoslavia in 1991, is blocking Macedonia’s hopes of joining Nato and the European Union.
Where does this leave Greece?
Mr Tsipras said he was moving immediately to a confidence vote.
His Syriza party has 145 seats in the 300-seat parliament and Mr Kammenos has called on his Independent Greeks party, which has seven, to vote against the government.
If the government loses, the next general election, due to be held in the autumn, could be brought forward.
The main conservative opposition party, New Democracy, also opposes the new name.
What’s the source of the dispute?
Present-day Macedonia and northern Greece were part of a Roman province called Macedonia and both claim the heritage of Alexander the Great two millennia earlier.
Greece’s objections forced the United Nations to refer to Macedonia as “the former Yugoslav Republic of Macedonia”.
Athens also vetoed Macedonia’s attempt to join Nato in 2008 – and blocked its EU membership ambitions.
Since 1991, many suggestions have been proposed, then rejected.
But a change of government in Macedonia in 2017 finally led to the deal reached last year.
Under the proposed agreement, the country’s language will be called Macedonian and its people known as Macedonians (citizens of the Republic of North Macedonia).
The new name will be used both internationally and bilaterally, so that even the 140 or more countries that recognise the name Macedonia will also have to adopt North Macedonia. In Macedonian, the name is Severna Makedonija.