"We will prepare all legal steps in the next weeks, and if or when the taxonomy takes effect, we will file legal action at the European Court of Justice," Environment Minister Leonore Gewessler told reporters.

She added Luxemburg had already said it would join the legal complaint against the commission's decision on the bloc's so-called "taxonomy" -- its classification of "green" energy sources.

"The decision is wrong because it endangers the future... We are giving our children a backpack full of problems... It's irresponsible," Gewessler said.

She described nuclear energy as "outdated" and "too expensive" and highlighted safety concerns and the uncertainty of how to deal with nuclear waste, calling the taxonomy "a greenwashing programme for nuclear energy and fossil fuels".

The European Commission defied protests from green campaigners and dissent in its own ranks to give a sustainable finance label to investments in both gas and nuclear power on Wednesday.

The EU executive argues that both have a role to play as cleaner power sources during the transition to a net-zero carbon future.