Iguala is a fixed sum that a person pays another periodically for services, “independientemente de la carga de trabajo” (regardless of the workload), according to the Diccionario del español de México.
Article 38 of the law on the professions in Mexico City states: “Los profesionistas podrán prestar sus servicios mediante iguala que fijen libremente con las partes con quienes contraten” (Professionals may provide their services through an iguala that they set freely with the parties who hire them).
In 1999, an article on medical fees in the Gaceta Médica de México cited the same rule for doctors.