In light of growing difficulties for schools to attract teachers in science, technology, engineering, and mathematics (STEM) fields and the continued discussions surrounding the unionization of education, this paper examines the effect of collective bargaining (CB) laws on the salary of teachers with a STEM degree. To isolate the effect of bargaining laws on STEM teachers, we compare pay differentials between STEM and non-STEM teachers in CB-mandated and -prohibited areas, controlling for the local labor market. Our results show that the bargaining laws increase female STEM teachers' salaries by approximately 7.5%.