The Football Supporters' Federation (FSF) has called on West Ham United to provide CCTV evidence to back allegations of misbehaviour against individual fans.
Last month, West Ham said 200 people faced football banning orders following violence during an EFL Cup game against Chelsea at the London Stadium.
Clashes broke out towards the end of the first derby match to be played at the ground, with seats and other objects being thrown.
But the FSF questioned the club's methods, citing the example of one fan who had his season ticket cancelled but was not told by the club what he had done.
The Times reported that a letter sent by the club and the stadium operator said: "In reference to the antisocial behaviour you displayed... in the event that you enter the stadium unlawfully you will be apprehended and prosecution may follow."
The FSF said the failure of West Ham to fully disclose what individuals were alleged to have done wrong meant they could not easily appeal against bans.
West Ham have said an independent appeal committee will be set up.
But the FSF said: "How can a fan reasonably appeal when it's not clear what they've done? We feel strongly that fans should get a proper process."
The organisation added that if individuals were proven to have thrown objects, it would become "a criminal and police matter."