Arsenal have indefinitely banned a fan for "offensive and inappropriate" tweets posted online.
The Gunners were alerted to the discriminatory tweets by Kick It Out - which praised the club for their actions - and a copy of the letter sent to the unnamed fan has since been posted on social media.
Arsenal have confirmed that the letter is genuine and warned other supporters that similar bans await anyone else posting discriminatory messages online.
Kick It Out, football's equality and inclusion organisation, has been running a social media campaign called 'Klick It Out' as it looks to curb the sharp rise in online discrimination.
"The tweets were brought to our attention by Kick It Out and our position is that we do not tolerate discriminatory language or behaviour of any description," an Arsenal spokesman told Press Association Sport.
"We work closely with Kick It Out to monitor these things and we identified him as being a previous member of Arsenal which is how we located his details. The message is zero tolerance against discriminatory behaviour. It is good to get that message out there."
It is believed the Klick It Out campaign has helped lead to 11 bans handed out by clubs to supporters during 2015-16 - and Anna Jonsson, Kick It Out's reporting officer, commended the decision taken by Arsenal.
"We welcome the strong action taken by Arsenal Football Club following reports of social media discrimination by a small number of supporters," she said in a statement released to Press Association Sport.
"As a third-party reporting bureau who brought the discriminatory posts to the attention of the club, we do not have the authority to impose stadium bans or other sanctions on supporters, but instead rely on clubs to implement punishment as they see fit.
"Social media discrimination within football has significantly increased and the reason we're running our 'Klick It Out' campaign is to raise awareness of online discrimination and how people can report such incidents. We encourage supporters to report any discrimination they see.
"It's credit to Arsenal in this case for taking action and sending out a message to supporters that discrimination of any kind won't be tolerated."
:: For more information on Kick It Out's social media discrimination campaign, visit www.klickitout.org.