Charlton draw with Northampton Town in front of11,500 fans
The fan of the League One club was given the warning in a letter, which has been widely shared on Twitter.
Charlton claimed that only one letter was sent and that they met with the fan on Thursday.
He has now been given his ticket after apologising for abusive behaviour towards the club and some of its staff.
The letter suggested the fan would need to agree not to post "derogatory or inflammatory comments" about the club on social media and sign an 'Agreed Behavioural Contract'.
But Charlton said he was given his ticket without signing the contract because of his apology.
It follows repeated protests by Charlton fans against owner Roland Duchatelet's running of the club, including disrupting matches at The Valley by throwing beach balls and stress balls onto the pitch.
Duchatelet, a main shareholder at five football clubs, took charge of Charlton in January 2014.
In that time, he has overseen six managerial changes and the club's relegation from the Championship last season.
Since Duchatelet's takeover of the Addicks, protest group CARD (Coalition Against Roland Duchatelet) has been formed from an umbrella of Charlton supporters' groups.
Organiser and lifelong club supporter Alan Davis told BBC Sport he was concerned the letter may be "the thin end of the wedge from the ownership".
He said: "It might be the start of more to come. We know season ticket sales are down this year and I have not renewed myself for the first time in more than 20 years.
"CARD are not seeking to disrupt matches during August, but we will continue to protest.
"As a group, we developed a slogan that Charlton has become 'the club that hates its fans'."
Charlton have yet to win a league game this season after drawing 1-1 with Northampton in front of 11,500 at The Valley on Saturday.