We examined whether institutional pressures explained sustainable company behavior based on sustainable Human Resource Management. Additionally, given that company voluntariness is a key factor of sustainable behavior, we analyzed the role of organizational engagement in employees. A sample of 206 firms in the chemical and chemical manufacturing industries as well as in the base metal manufacturing sector was used to test the hypotheses, using Partial Least-Squares Structural Equation Modelling. Our findings suggest that institutional pressures explain sustainable Human Resource Management and that organizational engagement mediates the relationship between institutional pressures and sustainable Human Resource Management. Moreover, a circular relationship develops that may play an even more pivotal role at the early stage of the diffusion of these practices.