If the bloc continues to work with the proposal and implements it, then Vienna will take legal action, says Austria's Environment Minister Leonore Gewessler.
Austria has been gearing up to fight the EU 'green' nuclear energy plan, including with a legal complaint.
The report came on Wednesday as the bloc moves to label energy from nuclear power and natural gas as green investments.
"Neither of these two forms of energy is sustainable and therefore has no place in the taxonomy regulation," Environment Minister Leonore Gewessler said in an interview with AFP news agency.
"If the Commission continues to work with this proposal and implements it then it is clear that we will take legal action," the Green politician added.
The 44-year-old said Austria had "very, very strong arguments" why energy from nuclear power and natural gas should not be labelled as green and as such she had "great confidence" a complaint at the EU Court of Justice (ECJ) could succeed.
"The question of waste disposal (from nuclear energy) has not been solved for decades...It's as if we give our children a backpack and say 'you will solve it one day,'" she said.
The European Commission is consulting with member states and European lawmakers until Friday on its plans.
A final text could be published by end of the month and would become EU law effective from 2023 if a majority of member states or the EU Parliament fail to oppose it.
Austria — which since 2020 has been governed by its first conservative-Green coalition — is also lobbying other member states, including Germany, to oppose the commission's proposal. So far, Luxemburg has indicated it would support a legal complaint, Gewessler said.
"Whatever is labelled green, whatever is labelled sus tainable must also actually contain green and sustainable investments," she said, adding renewable energy was "cheaper, more readily available and a safer and better alternative to nuclear energy".
Austria itself has only one nuclear power plant at Zwentendorf on the banks of the Danube river about an hour's drive from Vienna — and that one was never used.
The Alpine nation of nine million people has been fiercely anti-nuclear, starting with an unprecedented vote by its population in 1978 that prevented the plant — meant to be the first of several — from providing a watt of power.
Zwentendorf lay idle for several decades before it was taken over by Austrian energy company EVN, which maintains it as a training facility for international nuclear engineers. The plant finally began producing electricity in 2009 — by installing solar panels.
Austria itself targets that all electricity should come from renewable resources by 2030. More than three-quarters already comes from renewable sources.