The U.S. Supreme Court's 2018 decision in "Janus v. American Federation of State, County, and Municipal Employees" (AFSCME) (referred to as "Janus" hereafter) prohibited state and local government worker unions from negotiating collective bargaining agreements with fair share fee arrangements. In this report, the authors examine state collective bargaining restrictions on public-sector unions and how they impact spending on teacher compensation. Specifically, the authors develop a framework to estimate how spending on teacher compensation was affected by changes in the legal institutions (laws, court decisions, and other administrative mechanisms) governing public-sector unions in five states that experienced these changes early in the previous decade. There are two purposes of this study. First, the framework and the analysis, with the necessary adjustments to scale, contexts, and timelines, could be used in the near future to understand and estimate the impact on public-sector workers of the "Janus" decision (or of laws, court decisions, and other administrative mechanisms of a similar nature). Second, the results also set the stage for other important and broad questions regarding the affected education systems. These institutional changes that influence districts' spending on teacher compensation may also shift the career decisions of individuals who otherwise may have chosen a teaching profession, and they may have implications for student outcomes. Thus, this study can help policymakers better grasp the role of teachers unions in the post-"Janus" era by exploring pre-"Janus" events that affected the educational sector. The authors find that the pre-"Janus" legal changes weakening teachers unions in Idaho, Indiana, Michigan, Tennessee, and Wisconsin effectively reduced spending on total teacher compensation by about 6%, reduced teacher salaries by about 5%, and reduced teacher benefits by 9.7%. Even though it is not possible to use these results to exactly estimate the impact of "Janus" on union and nonunion teachers (nor to assess the impact of any other policy changes in states occurring within different contexts and under different timelines), the evidence from the study serves as an early warning of potentially negative repercussions of "Janus" on similar outcomes.