Greece argues that the name "Macedonia" implies a claim on the territory and ancient heritage of its own northern province of the same name, the birthplace of Alexander the Great.
The head of Greece's main opposition party says he will submit a motion for a no-confidence vote in the government later Thursday, objecting to a deal reached between the prime ministers of Greece and Macedonia to settle a decades-old dispute over Macedonia's name.
For his part, Tsipras, who "welcomed" the motion, hinted that the confrontation over the deal will be a major one.
Zaev and Tsipras agreed earlier this week that the former Yugoslav republic should be renamed North Macedonia, ending a disagreement that had prevented it from joining global institutions such as NATO and poisoned bilateral relations since the early 1990s.
Greek conservative New Democracy party leader Kyriakos Mitsotakis addresses lawmakers during a parliamentary session, where he submitted a motion of no confidence against Prime Minister Alexis Tsipras in row over a deal on neighbouring Macedonia's name, in Athens, Greece, June 14, 2018.
"We are all up against history", he said, adding that the motion seeks to prevent an unprecedented institutional derailment of the country, as it is unclear whether the SYRIZA-led government has the necessary parliamentary majority to ratify the deal.
The expected signing of the long awaited "name" deal between Macedonia and Greece will be just the first in a series of carefully planned steps on the potentially bumpy road towards its implementation.
Macedonia's president has refused to sign a historic deal that would change the country's name. I will not legalise political illegal agreements. Ivanov would have to sign off on the agreement if it is passed a second time.
Up to 1,500 people held a peaceful protest while chanting "traitors" outside Macedonia's parliament in Skopje late Wednesday.
With ANEL leader Panos Kammenos saying he will oppose the deal when it comes to Parliament, it is clear that Tsipras will have to rely on support from other political parties for its approval. Greek opponents of the deal were planning a protest in Athens Friday, when Tsipras is set to brief parliament on details of the deal.