There are fears that Saturday's Scudetto showdown with Inter could be suspended if supporters aim racist insults at Mario Balotelli.
"We want the two games against Inter and Bayern Munich to be a battle on the field and a party off it, with heated and passionate support," read the letter.
"But it must never be excessive or, worse, offensive. As for us, we are facing the next few days with the effort and pride of the big appointment.
"Know that Juventus have the duty to step on to the field with a single objective: to win.
"At the same time, we are fully aware of the importance that our fan clubs have for us. Your support, the clean style of cheering on Juventus in every game around the country, will be the best way to give us an extra push and the best response to those who are trying to paint all of our fans as uncivilised.
"I am certain that we will all together, players, club and fans, prove what the Juventus style really is."