Macedonia's president on Tuesday refused to sign a historic deal with Greece to rename his country the Republic of North Macedonia, after parliament ratified the accord.
Gjorge Ivanov had been expected to exercise his one-time veto as he is close to the country's nationalist opposition and has long opposed any compromise with neighbouring Greece.
The legislation will now go back to parliament to be ratified again and if it passes -- as is likely -- Ivanov can no longer block it.
The fallout from the Macedonia saga also continued in Athens after an MP quit the national-conservative Independent Greeks (ANEL) party, leaving the coalition government with 152 members in the 300-seat assembly.
Government spokesman Dimitris Tzanakopoulos said the resignation did not threaten the coalition.
"It remains stable" with 145 seats from the leftist Syriza of Prime Minister Alexis Tsipras and seven from ANEL, he said.
ANEL had already lost one MP ejected from the party on Saturday after voting for a censure motion against the government over the Macedonia deal.
'Dependent on Greece'
Both countries' foreign ministers signed a preliminary agreement earlier this month that aims to start unravelling one of the world's longest diplomatic disputes, which began 27 years ago with Macedonia's declaration of independence.
But Ivanov said in a statement: "I decided not to sign the law on the ratification of the agreement with Greece.
"The agreement makes Macedonia dependent on another country, in this case Greece."
Athens had for years objected to its neighbour being called Macedonia because it has a northern province of the same name, which in ancient times was the cradle of Alexander the Great's empire -- a source of intense pride for modern-day Greeks.
Tsipras has been accused of treachery by hardliners, but last week defeated the censure as police and protesters clashed outside parliament.
Macedonia's main opposition party, the nationalist VMRO-DPMNE, has repeatedly said it will fight the change of "Macedonia's constitutional name", arguing it erodes the country's identity.
Once the Skopje parliament ratifies the deal for the second time it will be put to a referendum to be held at a later date.
Macedonia's Social Democrat Prime Minister Zoran Zaev has said he would resign if the agreement is not supported in the referendum.
If the public do back the name change, Macedonia's government will then have to change the constitution -- a key Greek demand before its own parliament is asked to ratify the deal.
In exchange for the name change, Macedonia hopes to secure a date to begin European Union accession talks at a summit this week as well as an invitation to join NATO in mid-July.
Due to the dispute with Greece, Macedonia was admitted to the United Nations in 1993 under the provisional name of the "Former Yugoslav Republic of Macedonia".