The legal cases could eventually land the two member states in the bloc’s highest court.
A Hungarian political outsider with no party affiliation will run against Prime Minister Viktor Orban in next year’s parliamentary election after winning an opposition runoff primary on Sunday.
Small-town conservative Peter Marki-Zay defeated left-wing Klara Dobrev who pledged to support him at the head of an alliance of six opposition parties.
“We can only win together,” Marki-Zay told cheering supporters with his wife and seven children standing behind him.
“This was a battle, but we have to win the war as well,” he said, referring to the 2022 election.
The vote, which will determine the 199 seats of the Hungarian Parliament, is expected to be held by April.
Dobrev conceded defeat and sided with his former opponent. “I wish him a lot of strength … in our effort to unseat Viktor Orban and then dismantle his regime,” he told a news conference.
While final results were due later on Sunday, Marki-Zay’s lead appeared unassailable. With 60 percent of the votes counted, he was leading by a margin of about 58-42 percent.
Marki-Zay’s family-man image and Christian faith could appeal to lots of undecided voters. He has sought to portray himself as a palatable choice for both left-wing and conservative voters, campaigning on leading a coalition of “the clean” and promising to root out corruption.
Opinion polls show Orban’s conservative Fidesz party and the opposition alliance running neck-and-neck.
An economist and engineer who lived in the United States and Canada for five years, Marki-Zay rose to prominence in 2018 when he won a mayoral contest in his southern hometown, Hodmezovasarhely, a Fidesz party stronghold.
For the first time since coming to power in 2010, Orban will face a united front of opposition parties that includes the Socialists, liberals and the formerly far right, now centre right, Jobbik.
While Orban has had a series of disputes with the European Union, Marki-Zay is looking to improve relations with Brussels and is in favour of Hungary adopting the euro in the foreseeable future.