Staunchly anti-nuclear Austria said on Friday it had followed through on a pledge to file a legal challenge to the European Union’s inclusion of natural gas and nuclear energy in a list of “green” investments.

At issue is the European Union’s so-called taxonomy, a rulebook defining which investments can be labelled climate friendly and designed to guide investors toward green projects that will help deliver the bloc’s emissions-cutting targets.

The European Parliament approved the European Commission’s proposal in July, paving the way for it to pass into law and prompting Austria to confirm that it would challenge it in the European courts as it had warned for months. Luxembourg said it would support Austria’s move.

“Nuclear energy and gas are neither green nor sustainable,” Austria’s environment minister, Leonore Gewessler of the Greens, said in a statement. “We have therefore filed a legal challenge against the European Commission’s taxonomy regulation, as we said we would.”

Gewessler will hold a news conference on Monday to provide details on the legal challenge filed at the Court of Justice of the European Union.

The EU taxonomy aims to clear up the murky world of sustainable investing by ensuring any financial products making eco-friendly claims meet certain standards. Gas-fuelled plants, for example, must switch to low-carbon gases by 2035 and meet an emissions limit.

Greenpeace and other environmental groups have already filed their own legal challenges to the inclusion of nuclear energy and natural gas.