Panos Kammenos's Independent Greeks party objects to a deal reached with neighbouring FYR Macedonia over a long-standing name dispute.
Greek Prime Minister Alexis Tsipras will undergo a confidence vote on Wednesday after his coalition partner quit over a long-standing name dispute with neighbouring country FYR Macedonia.
Panos Kammenos, whose Independent Greeks party props up Tsipras minority government, announced his resignation on Sunday morning after a meeting with Tspiras.
"The Macedonia name issue...doesn't allow me not to sacrifice the minister's chair," Kammenos said.
He added that the party's other ministers will also walk out.
Tspiras told reporters after the meeting that he has "informed the president of the parliament that we will immediately move to the process outlined by the constitution for the renewal of the confidence in my government.
Kammenos has already stated that the Independent Greeks would not support the ruling Syriza party.
Greece has a parliamentary election scheduled for October and Syriza is currently trailing the centre-right New Democracy party, which also opposes the deal with FYR Macedonia, by 12 points.
"Tsipras is expected to win both the confidence vote and the vote on the Macedonia deal. Kammenos, the leader of ANEL, may have withdrawn his support, but more than half of his MPs will continue to support the government," Angelos Chryssogelos, research fellow from Chatham House told Euronews.
"Strikingly he is not whipping them on the vote of confidence on Wednesday, a first for any party in such a vote. There is thus speculation that even though formally the coalition has broken off, it is basically a choreographed disagreement, whereby Kammenos is allowed to oppose the Prespa agreement while 'lending' MPs to Tsipras for him to stay in power - and vote in Prespa of course," Chryssogelos added.
What's the dispute about?
Athens has for decades objected to the Former Yugoslav Republic of Macedonia's (FYROM) use of the word "Macedonia," arguing it suggests Skopje has territorial claims on the Greek border region of Macedonia.
The disagreement, which came to the fore after the smaller country gained its independence from Yugoslavia in 1991, has seen Athens block multiple attempts by Skopje to join Nato and the European Union.
The geopolitical stalemate appeared to come to an end in June 2018 when the two countries announced that an agreement had been found to rename FYROM the Republic of Northern Macedonia.
94% of voters in FYROM then backed the deal with Greece in a referendum which was later invalidated because turnout had been too low. The country's parliament nevertheless ratified the deal in a vote on january 11.
Greeks MPS were expected to also hold a vote in the coming weeks.