We analyse a reform of notice periods for employer-initiated separations in Sweden, which reduced the notice periods for newly hired older workers substantially but implied minor or no changes in the advance notices for younger workers. The reform was initiated at different times depending on collective agreement. These circumstances provide ample opportunity for the identification of its effects. Our findings indicate heterogeneous effects on hirings and separations across collective agreements. A salient feature of the results is that the estimated effects increase with the treatment dose, i.e., the size of the reduction in notice periods across different age groups.