Without a union, employers can change your pay and working conditions at any time as long as they do not violate certain laws, like the minimum wage. Once you form a union, your employer cannot make changes in your working conditions unless they are negotiated with you as union members.

A 2011 study of teachers unions found that collective bargaining increased starting salaries by 3.9 percent, and added an additional 5.4 percent over the first five years of a teacher’s career.