Austria’s new government, an alliance between Chancellor Sebastian Kurz’s conservatives and the far-right Freedom Party, has pledged to continue Vienna’s decades-long policy of opposing nuclear power.
Austria would be affected if there were to be a nuclear disaster at the atomic power plant.
The Paks plant was built with Soviet-era technology in the 1980s during Hungary’s communist period.
The minister for sustainability and tourism, Elisabeth Koestinger, said: “We must take up this David-versus-Goliath struggle for the sake of our nature, our environment and our unique countryside.
“Nuclear energy has no place in Europe. We will not deviate from this line by even a centimetre.”
A spokesman for the EU executive said: “The Commission will defend its decision in Court.”
Last year, EU state aid regulators approved Hungary’s plan to build two new reactors at its Paks nuclear site with the help of Russia’s Rosatom, saying Hungarian authorities had agreed to several measures to ensure fair competition.
The two new reactors will double the plant’s nominal capacity of 2,000 megawatts.
Hungary aims to start construction on the reactors this year, with the first facility expected due to becompleted in 2025.
Austria has used the argument that nuclear energy expansion is not the best way to deal with climate change and expansion is not in the “common interests” of the European Union.
Ms Koestinger said: “EU assistance is only permissible when it is built on common interest.
“For us, nuclear energy is neither a sustainable form of energy supply, nor is it an answer to climate change”.
The construction of two new reactors at the site is part of a 2014 deal struck between Hungary’s right-wing Prime Minister Victor Orban and Russian President Vladimir Putin.
Since the 1970s, Austria has been very anti-nuclear, which began with a vote by its population that prevented the country’s only plant from providing a watt of power.
Austria filed a complaint against EU-approved state aid for the Hinkley Point C nuclear plant in the UK in 2015, saying that atomic energy was unsustainable and high-risk.
Hungarian Prime Minister Viktor Orban’s office said in a statement: “The Paks nuclear plant is the guarantee for providing a cheap, reliable and safe supply of electricity to Hungarian people and businesses.
“Therefore, the Hungarian government will stick to its plan to ensure the maintenance of capacity at the Paks plant,” it said, adding that the lawsuit would not affect work on the project.
The European Court of Justice in Luxembourg usually justifies what the European Commission has already decided.