John Ruiz, Ceo of the Our Firefighters Children's Foundation, booked the pair to headline his Stop The Violence, Save The Children show in New York on Saturday (17Aug13).
He later discovered they were also signed up for a similar show on Staten Island just weeks later, violating a non-competition clause in their contract, so he cancelled the gig.
Now Ruiz is demanding the two rappers hand back the $15,000 (£10,000) they were each paid in advance for the show, insisting his foundation has been left $120,000 (£80,000) out of pocket over the axed concert.
He tells the New York Daily News, "The contract said they couldn't perform within 30 days of my concert in an 80-mile radius. They didn't do what they were supposed to do. Once they got the money, they were gone."
A spokesman for Fabolous alleged they were not given any officials forms by Ruiz, but refused to comment when asked if the rapper would be returning the $15,000 down payment. A representative for French Montana did not reply to requests for comment. Meek Mill, who was also on the bill, has returned his payment.
The cancelled show was scheduled to take place at the United Palace in Manhattan. Our Firefighters Children's Foundation provides kids in the Big Apple with affordable educational via theatrical performances.