Article L8221-1 of the French Labour Code
The following are prohibited 1° Total or partial concealment of work, as defined and performed under the conditions set out in Articles L. 8221-3 and L. 8221-5; 2° Advertising, by any means whatsoever, tending to knowingly encourage concealed work; 3° Knowingly using, directly or through an intermediary, the services of a person engaged in concealed work.