The card game bridge is a sport and should be exempt from VAT, according to an opinion by the top advisor to the European Court of Justice.
In an ongoing case brought by the English Bridge Union, advocate-general Yves Bot said it was a sport because it required mental effort as part of a challenge.
EU law has no definition of sport beyond excluding games of chance.
The comments are not legally binding, but are normally followed by UK judges.
HM Revenue and Customs had refused to reimburse the English Bridge Union for VAT payments on entry fees to tournaments.
A spokesperson for the tax collection agency said: “HMRC is considering the advocate general’s opinion and awaits the final decision of the [court].”
EU law requires proof of benefits to physical or mental well-being for a sport to claim VAT exemption.
So-called duplicate bridge, a form of contract bridge, is considered a sport by the tax authorities of Austria, Denmark, France, the Netherlands, and Belgium, but not by Ireland and Sweden.
It is played by pairs of people in fours in clubs, tournaments, and online, and was classified as a sport by the International Olympic Committee in 1998.
In the run-up to the referendum the European Court of Justice faced criticism from Leave campaigners, who said the UK lost most of its cases to the court.
However, the court has backed Britain on cases involving challenges to British welfare rules, and has upheld sanctions on Russia that Britain supports.