The U.S. labor movement is bracing for a decision by the Supreme Court that could dramatically weaken public sector unions. The case, Janus v. American Federation of State, County, and Municipal Employees, Council 31, et al., is expected to be decided in a vote against “fair share” fees in the public sector. The ruling would strike down a 41-year precedent (Abood v. Detroit Board of Education, 1977) that requires public sector workers represented by a labor union to pay for the collective bargaining work that the union performs on their behalf. If the Court strikes down Abood, workers would be able to “free ride” and receive services, benefits, and representation from unions without paying for them in the form of fair share fees or membership dues. This would impact at least 5 million state and local government employees represented by collective bargaining agreements in 23 states and the District of Columbia. This report projects the negative impact of overturning fair share including an annual drop in economic activity in the U.S. by $11.7 billion to $33.4 billion, a loss of $1,810 in wages per worker, and a decrease in teacher salaries of 5.4%.