Tottenham have banned three season-ticket holders after they attempted to sell their Champions League final tickets.
The three fans have been banned indefinitely after listing them on a "secondary ticketing platform".
The club, who face Liverpool in the final in Madrid on June 1, have also warned others doing the same even after collection.
Spurs said in a statement: "Once again, we wish to remind all our supporters that any ticket purchased is for the sole use of the individual that purchases it from the club.
"Transferring or selling tickets on unofficially breaches our terms and conditions and is against the law.
"We shall look to take the strongest possible action against anyone found to be engaging in such activity - including indefinite season ticket bans.
"Additionally - if we are made aware of tickets being sold on by supporters after collection we will cancel the original match tickets with UEFA and the Wanda Metropolitano Stadium in Madrid, meaning these tickets will no longer be valid for entry to the stadium.
"Please do not ruin one of the biggest occasions in the club's history by selling on your ticket and profiteering from fellow Spurs fans."
Liverpool are also investigating after they identified five supporters who are suspected of listing their Champions League final tickets for sale on secondary ticketing platforms.
A sanctions committee will look into the cases and the fans could be banned from Anfield for life if found guilty.