They are seeking damages of “a sum exceeding” $1bn (£790m).
In November 2022, Binance announced its first “CR7” collection of non-fungible tokens (NFTs) in partnership with Ronaldo, which the footballer said would reward fans “for all the years of support”.
NFTs are virtual assets that can be bought and sold, but which have no real-world form of their own – in other words they only exist digitally. Generally, they are used to mark ownership of something, such as a picture or video online.
In a social media video announcing the partnership, Ronaldo told would-be investors “we are going to change the NFT game and take football to the next level”.
The cheapest NFT from the collection was priced at $77 when it went on sale in November 2022 – but one year later, it was priced at about $1.
The claimants allege that Ronaldo’s promotion of Binance led to a “500% increase in searches” for the crypto exchange, which is registered in the Cayman Islands.
Nigel Green, boss of consultancy firm DeVere Group, said the problems at the heart of the case went wider than just one footballer.
“Instead, attention should also be directed towards global regulators who have been slow to establish clear guidelines for this evolving financial landscape.”
Neither have responded to the BBC’s requests for comment.
The class action suit was filed a week after the US Justice Department told the firm to pay $4.3bn (£3.4bn) in penalties and forfeitures.
It accused Binance of helping users bypass sanctions around the world, and of making it easy for criminals and terrorists to move money.