The group put the proposal before Parliament and said it is expecting a response from the parties by August 7. The EU agreement, the group said, limits Parliament's financial competence, Estonian sovereignty and the principles of democracy.

“We are convinced that the decision to give up Estonian sovereignty requires a public mandate,” the statement from the group said. “The question whether we are ready to transfer a certain part of our financial independence to Europe should be put to a public referendum.”

The five ex-Center Party members call themselves the Union of Democrats and are banded together under a nonprofit.

The treaty's accordance with the Constitution of Estonia was recently challenged by Chancellor of Justice Indrek Teder, meriting a review by the Supreme Court last month. Although the court cleared the agreement as constitutional, it was hotly debated and received nine dissenting opinions from a total of 19 justices who reviewed the case en banc.

Teder had argued that article four of the treaty, in establishing an 85 percent majority in votes regarding future emergency decisions, violated the the principle of unanimity and thus Estonian financial sovereignty.

“Although the contested article restricts the financial competence of the Estonian Parliament, the principle of rule of law and the sovereignty of Estonia, the restriction is justified,” a statement summarizing the Supreme Court's ruling said.

Ott Tammik