Article 20 of the Mexican Federal Labor Law
An employment relationship, regardless of the act that gives rise to it, is understood to be the rendering of subordinate personal work to a person in exchange for the payment of a salary.
Individual employment contract, whatever its form or denomination, is that by virtue of which a person is obliged to render to another a subordinate personal work, by means of the payment of a salary.
The rendering of work referred to in the first paragraph and the contract entered into produce the same effects.