ATHENS — Greek opponents of an agreement will let the neighboring Former Yugoslav Republic of Macedonia (FYROM) be called North Macedonia – keeping the name of an ancient Greek province – have sued, asking the deal declared unconstitutional.

The deal pushed by anti-nationalist Prime Minister and Radical Left SYRIZA leader Alexis Tsipras would also lift Greek vetoes on getting into NATO – even before FYROM changes its Constitution to remove irredentist claims on Greek land and opens the door to begin European Union entry hopes.

A group of organizations said it appealed to Greece’s Supreme Court to nullify the “nightmare” agreement as protests continued and Tspiras ignored surveys showing 62 percent of Greeks opposed.

The group argues that the preliminary agreement negotiated by the two countries’ prime ministers should have been ratified by Greece’s Parliament before it was signed by their foreign ministers.

It also maintains the deal could lead to changes to Greece’s northern borders, causes “irreparable damage to the Greek nation” and should have been preceded by a referendum.

FYROM’s Parliament ratified the deal before it goes to a referendum in the autumn but the country’s President, Gjorge Ivanov, refused to sign, meaning it will have to be approved again and, if so, the law requires he must consent. Tsipras has barred a referendum for Greeks.

Hardliners in both countries oppose the deal, saying it concedes too much to the other country but FYROM Premier Zoran Zaev said the referendum will get 75-85 percent approval.

(Material from the Associated Press was used in this report)