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 to<br />increasing 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 the<br />detriment 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 i...