Leading agents including Mino Raiola, Jorge Mendes and Jonathan Barnett have threatened Fifa with legal action over plans for a cap on transfer payments.In September, Fifa announced plans to limit agents of the selling club to a maximum of 10% of the transfer fee.In addition, Fifa want a 3% cap of the player's fee and 3% of the player's fee for agents of the buying club."We want fairness," Barnett countered. "Fifa should recognise us and treat us in a proper manner."Fifa want to implement their plans possibly as early as next season but Barnett, who represents high-profile players including Gareth Bale and England goalkeeper Jordan Pickford, added: "The truth is Fifa doesn't know exactly what an agent does."No-one from Fifa has ever been to my office or had a conversation with me."If you ask players what they want, they are in favour of agents. There are never complaints about agents' fees from players."We will try until the last minute to resolve the problem but rest assured, if necessary we will go to every court in the world."The agents were among a 200-strong gathering in Barnet.Raiola and Barnett were part of a smaller meeting beforehand, in which all agents present were said to be united in their opposition to Fifa's intentions."For the first time, we have agreed a united policy in respect of Fifa's proposals," said Mel Stein, life president of the Association of Football Agents."We will be writing to them jointly to advise them that once there is a formal, consultative process in place where all parties can bring their proposals to the table, we will be eager to meet with them."As far as we are concerned, it sends a clean, positive message to Fifa on where we are on this."The BBC has contacted Fifa for a response.