Barcelona, Real Madrid and two other Spanish soccer clubs will have to pay millions of dollars in back taxes, after Europe's top court upheld an appeal, in a win for EU competition enforcers fighting tax avoidance.

The European Commission in its 2016 ruling said the two clubs plus Athletic Bilbao and Osasuna enjoyed a 25 percent tax rate for more than 20 years, giving them an unfair advantage over the 30 percent norm for sports companies.

The four teams, which enjoyed the lower tax rate because they were treated as non-profit organizations instead of professional football clubs with limited liability, were ordered to pay up to $6 million each in back taxes.

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Barcelona subsequently challenged the EU decision and got the General Court to strike it down in 2019 on the grounds that the EU competition watchdog had not shown to the required legal standard that the measure conferred an advantage on its beneficiaries.

The commission then appealed to the Luxembourg-based Court of Justice of the European Union (CJEU), saying that the lower tribunal erred in putting a heavy burden of proof on enforcers to prove the clubs had an economic advantage.

CJEU judges agreed with its arguments.

Barca's annus horribilis

The decision comes with the club engulfed in an alleged scandal branded "Barcagate," in which money is alleged to have been given to a social media company to write damaging stories about the club's own players.

Club president Josep Maria Bartomeu decided to resign last fall due to growing discontent among fans and a vote of no confidence.

Police arrested Bartomeu along with other club officials and searched Barcelona's stadium on Monday as part of the investigation.

His departure comes with the club more than $1 billion in debt and Bartomeu has also seen the club fail to meet fans' expectations on the pitch and suffer some heavy defeats in the Champions League. 

Bartomeu's successor is due to be elected on Sunday, when club members will choose between the final three candidates, Joan Laporta, Toni Freixa and Victor Font.

Laporta, a former Barcelona president who is the front-runner in the race, said the arrests "diminish the reputation of the club."