National audienceThe proposals aiming at reducing or making more flexible job protection are built upon the hypothesis according to which firms are forced to adapt toincreasing uncertainty of demand and activity. Analysing firms' behaviour in French industry, this paper shows that the increase in sub-contracting resort is related less to a rise in uncertainty than to a substitution behaviour giving greater place to commercial contracts to thedetriment of labour contracts. In conclusion, strengthening labour legislation would improve protections of workers affected by those practices.Les propositions visant à alléger ou assouplir la protection de l'emploi se fondent sur l'hypothèse selon laquelle les entreprises font face à une incertitude a...