This study presents the results of 5,256 discrimination tests in access to employment, corresponding to more than 10,000 messages sent in 2018-2019 to 103 of the biggest French companies, based on the criterion of ethnic origin. Using an instrumental variable approach, we evaluate the effect on discrimination of the signing of diversity labels that validate the implementation of pro-diversity actions. We find significant and robust discrimination based on origin against the presumed French North African candidates: the positive response rate for North African applicants is on average 27% lower than that of French applicants. We show that companies that engage in pro-diversity actions have a lower level of ethnic discrimination and that the diversity label has an effect per se on discrimination: the implementation of pro diversity actions reduces by 1.8 percentage points the probability for a firm to advantage the French origin applicant.