VIENNA (Reuters) - Austria's ruling coalition of conservatives and Greens flirted with collapse on Monday after a minister went it alone to tip the balance in the European Union in favour of a nature restoration law, but the alliance will limp on.

Environment Minister Leonore Gewessler of the Greens shifted Austria's position at the last minute over the conservatives' objections to cast the country's vote in favour of the bloc's flagship policy to restore damaged nature at a meeting of her counterparts in Luxembourg on Monday.

That incensed Chancellor Karl Nehammer and his conservative People's Party (OVP), who said Gewessler was legally required to obtain the agreement of the OVP-run Agriculture Ministry since it is partly responsible for the issue. The OVP opposes the law.

"The Green coalition partner has shown its true face. On the one hand it is endlessly pontificating. On the other, it is prepared to put ideology before the constitution and the law," Nehammer told a news conference in Brussels.

The coalition partners have clashed before on hot-button issues like immigration, but this case was particularly bitter.

The OVP said it would launch a criminal complaint against Gewessler for abuse of power and bring a legal challenge to the European Court of Justice seeking the annulment of Monday's decision. Gewessler argued the law is on her side.

"With such flagrant misconduct by a minister belonging to a coalition partner, the coalition should be ended," Nehammer said, before adding: "I will not do that."

The coalition has already called a parliamentary election for Sept. 29, at the end of the current five-year parliament. While it is unlikely that date could have changed, Nehammer said he wanted to ensure smooth government in the months until then.

Greens leader Werner Kogler, who is Austria's vice chancellor, said he was confident that could happen.

"We still have a lot to do. Now is not the time for barbs or disputes. It is the time to act," he told a news conference.

(Reporting by Francois Murphy; Editing by Marguerita Choy)