UEFA's decision to partner with a company selling cryptocurrency fan tokens has been described as "incomprehensible" by Football Supporters Europe.
A day after being praised for giving away tickets to its men's and women's club competition finals, European football's governing body has been heavily criticised over a new agreement with Socios.com.
The sale of fan tokens - which can rise and fall in value - has been criticised as a means of monetising fan engagement, in a largely unregulated market.
FSE condemned the partnership, which sees Socios.com become UEFA's official fan token partner, and tweeted: "This is an incomprehensible move at a time when football needs protection from crypto-mercenaries.
"Governing bodies have a duty to protect the integrity & sustainability of football & everyone associated with it.
"There are countless ways to properly engage with fans. Encouraging fans to invest in 'fan tokens' isn't one of them. They only serve the interests of those selling them."
Socios.com sells branded fan tokens to supporters of clubs and bodies they have a commercial agreement with. Supporters must convert their money into a cryptocurrency called Chiliz.
Each token allows users to exercise voting rights over matters related to their club, but one of the criticisms of the tokens is that these votes are often on relatively trivial matters.
Token holders also have a chance to win club-related prizes, while the tie-up with UEFA promises rewards such as VIP trips to UEFA events, the chance to visit the organisation's headquarters and to meet 'UEFA legends'.
The value of tokens can rise and fall depending upon supply and demand, potentially leaving fans out of pocket.
UEFA's marketing director Guy-Laurent Epstein said: "Thanks to this new alliance, hundreds of millions of fans around the world will have the opportunity to become more than spectators and play active roles in the biggest club football competitions on the planet through fan tokens."