The Brazilian football champions have asked fans and players to curtail an internet campaign in which they take and post pictures dressed as Taliban fighters, in an attempt to "show their warrior spirit."
Fluminense fans were so disappointed with the side's defeat in a Copa Libertadores match that they used Twitter to ask players and other fans to and join the campaign.
Since then several players, including Brazil striker Fred, have posted photos with their faces partially covered by scarves with the club's colours.
In a statement, the club says the initiative glorifies terrorism.
Fluminense are known by their fans as "a team of warriors".
The statement read: "The intentions of those who began this movement and have joined it clash with the Taliban's image, who are terrorists and not healthy warriors. That is why Fluminense Football Club denounces this campaign."
The club described the "Be a Taliban warrior" campaign as a "call for violence".