A Charlton fan was told that he would only receive his season ticket if he signed their “Agreed Behavioural Contract,” which would prevent him from speaking out against the way the club is being run.

The letter, sent to the fan on August 2 but released online yesterday on Twitter, sparked outrage among football fans who have described it as the club’s way of clamping down on the protests surrounding the way the club is run.

The letter tells the fan that due to “some of the issues that we unfortunately experienced towards the end of last season,” he would only be allowed back in if he agrees to “refrain from posting derogatory or inflammatory comments” on social media or carrying out “any other form of behaviour that could be deemed to be of an anti-social nature.”

Stan Collymore called for “a full boycott of the Charlton supported by the Football League, FA and fans of other clubs,” while one user on Twitter stated that: “Charlton [have] started blackmailing fans with their season tickets to stop them protesting against the board.”

Another echoed that tweet, saying: “Wow. Charlton threaten to take fan’s season ticket away over negative comments about club on social media.”

The club said in response to the backlash that only one letter was sent after the individual apologised for the comments and the season ticket was handed over without any such agreement being signed.

However, they also revealed that this isn’t the first time they have made fans sign this type of agreement, in order to stop foul and abusive language aimed at the club.

“In this instance, the club called the meeting to explain the Agreed Behavioural Contract process with the individual and the reasons behind it,” said a statement. “It was emphasised that the meeting was not due to any involvement with supporter protests but solely in response to his continuous, personal behaviour and abuse.

“The meeting ended amicably and, as he appeared sincere in his apology, the club handed the individual his 2016/17 season ticket and he was not asked to sign an Agreed Behavioural Contract.”

The fan denied that he had been aggressive, telling the Guardian that “all I’ve been saying is we want our club back.”

The atmosphere at The Valley has become increasingly hostile since Belgian Roland Duchatelet became Charlton’s owner in January 2014.

Attendances have gradually dwindled owing to perception of how the club has been run, amid a series of disastrous managerial appointments after the sacking of Charlton favourite Chris Powell.

Duchatelet and club chief executive Katrien Meire have been the target of much of the fans’ frustration, which was worsened by last season’s relegation from the Championship to League One.

A protest has been planned by fans for today’s match outside the Charlton badge outside the North Stand, starting at 1.30pm.