FIFA has filed a criminal complaint in Switzerland against secondary ticket seller Viagogo over tickets for this month's World Cup.
Football's world governing body says it has received numerous complaints from consumers and consumer sites over the past few months.
FIFA says fans who buy through unofficial platforms, including Viagogo, for World Cup games in Russia face being denied entry to stadiums and that it would cancel all tickets it identified as being traded through unauthorised sellers.
MoneySavingExpert founder Martin Lewis has urged people not to buy tickets from Viagogo, and last week the advertising watchdog the Advertising Standards Authority said the website was breaking UK ad rules after missing a deadline to make compulsory fees sufficiently clear on its website.
We have contacted Viagogo for comment and will update this story if we hear back.
See our Cheap Tickets guide for what to watch out for when buying cheap theatre, sport and gig tickets.
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How much are World Cup tickets on Viagogo's website?
According to the Press Association, Viagogo's website was still selling World Cup tickets earlier today, including single seats for the 14 June opening game at more than double face value.
A category three ticket, the cheapest available to non-Russian residents, for Russia vs Saudi Arabia in Moscow was priced at 474 Swiss francs (£360). The same ticket bought originally through FIFA's website would cost 220 dollars (£165).
Viagogo notes on its World Cup sales page "prices are set by sellers and may be lower or higher than face value. Prices exclude booking and delivery fees."
What does FIFA say?
On its website it says: "FIFA's ultimate objective in the fight against the secondary ticket market is to prioritise the safety and security of fans and enforce a fair 2018 FIFA World Cup ticketing pricing scheme.
"FIFA reminds all fans that Fifa.com/tickets is the only official and legitimate website on which to buy 2018 FIFA World Cup tickets.
"Tickets purchased via unauthorised distribution channels, including all tickets purchased through Viagogo AG, will be cancelled once identified. FIFA reserves the right to refuse entry to the stadium to any holder of such tickets.
"During the 2018 FIFA World Cup Russia, FIFA and local authorities will conduct strict admission checks."
Additional reporting by Press Association.