The breach relates to the transfer of Dale Stephens, who joined Brighton from Charlton Athletic in January last year.
An FA statement declared that agents Alex Levack, Matthew Kleinman and Ali Rahnama have all been sanctioned and warned as to their future conduct after admitting to breaking the rules.
Levack and Kleinman have both been fined £7,500 and "suspended from all agency activity and intermediary activity for a period of 14 months".
Half of that suspension comes into force immediately, with the other half suspended for a period of 12 months.
Rahnama, meanwhile, has been suspended from all agency activity for nine months, three of which is to be served immediately with the remainder suspended.
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