(Bloomberg) -- The future of Irish politics lies in the hands of about 2,500 Greens.

The Greens will today announce whether its members have back a proposal to enter coalition with the nation’s traditional parties of government, Fine Gael and Fianna Fail. Two thirds of party members must back the deal to allow it join the nation’s first grand coalition. A result is due between 6pm and 7pm in Dublin.

“Two thirds is a high bar,” said Eoin O’Malley, a politics professor at Dublin City University. “But I’m inclined to think it will sneak through.”

If the Greens sign up, Fianna Fail’s Micheal Martin will become prime minister until the end of 2022, before Leo Varadkar moves back into the top job. Should the Greens reject the deal, the nation could face another election within months. Fine Gael and Fianna Fail have so far refused to negotiate with Sinn Fein, which won the biggest share of votes in February’s election, because of its former links with terrorism and left-leaning policies.

The Greens are only now recovering from their last brush with power. The party governed with Fianna Fail from 2007 to 2011. After the Irish economy collapsed, the party lost all six of its seats.

Led by Eamon Ryan, the party won 12 seats in February’s indecisive general election, leaving it as king maker.

The deal agreed by the three parties has been attacked by some Greens for not doing enough to deal with issues including carbon emissions and housing. Greens lawmaker Frances Noel Duffy, for example, plans to reject the deal, which was negotiated by his wife Catherine Martin - the party’s deputy leader.

The proposed deal means “it looks like we’re heading for another bout of austerity,” party member Tate Donnelly who ran for parliament in the election, said in a video posted to Twitter. A planned carbon tax “will be regressive” and “put people into poverty,” he said.

In a sign of the stakes at play, the Green leadership enlisted U.S. actor Mark Ruffalo to lobby its members to back the program for government.

“Don’t fret about not getting everything you want right at the moment,” Ruffalo said at a Green Party online conference. “Do what’s right for right now.”

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