In 2010, Megan Sampson was named an Outstanding First Year Teacher in Wisconsin. A week later, she got a layoff notice from the Milwaukee Public Schools. Why would one of the best new teachers in the state be one of the first let go? Because her collective-bargaining contract requires staffing decisions to be made based on seniority.

Ms. Sampson got a layoff notice because the union leadership would not accept reasonable changes to their contract. Instead, they hid behind a collective-bargaining agreement that costs the taxpayers...