Across the globe, men make markedly more money than women, even within the same position. We introduce egalitarian norm messaging as a potential intervention to increase women’s salaries and counter the gender pay gap. In two preregistered experiments with seasoned professionals (N = 435, work experience: M > 8 years, salary negotiations: M > 18 per year), we find a significant gender pay bias—HR experts offered markedly lower salaries in an online negotiation to (simulated) female versus male candidates with identical qualifications. Moreover, the experiments show that dynamic (Experiments 1a and 2), as well as static egalitarian norm messages (Experiment 1a) increased salary offers to women. Exploratory mediation analyses suggest that the dynamic egalitarian norm effect was driven by HR professionals’ feeling of working towards a shared goal of greater equity. A message that merely increased awareness of the pay gap did not elicit this feeling and did not significantly increase salary offers to women but resulted in fairly equal treatment of men and women (Experiment 2). While the egalitarian norm intervention significantly increased salary offers to women, it also unexpectedly reduced offers to men, thereby reversing the gender bias (Experiment 2). We discuss the theoretical contribution with regard to gender pay bias and egalitarian norm interventions, as well as applied implications.