The striker joined the Latics on a free transfer last summer, but the Football Association have found irregularities involving the player and agent, Wille McKay
Fortune joined the Championship outfit on a free transfer last summer after leaving West Brom, signing a two-year deal.
The punishment relates to a breach of the FA's Football Agents Regulation C10(a)(i), which states an agent "must not carry out any activity for or on behalf of a club in any transaction in respect of a player where the agent has carried out any activity for or on behalf of another club in respect of the same player in the immediately preceding completed transaction or contract negotiation of that player".
The striker's agent Willie McKay has also been punished by the FA, having his overseas agent registration suspended for nine months.
An appeal could see the Scot's ban overturned and in any case it will not come into effect unless he offends again in a two-year period.
Fortune has made 48 appearances in all competitions for Wigan this season, scoring five goals.