Further evidence that pay transparency serves to reduce the gender pay gap comes from unions.

According to the Institute for Women’s Policy Research, women in union jobs earn 31 percent more per week than women in nonunion jobs.

Why? In part, unions are able to use the power of collective action to fight for higher wages overall. But unions also provide their members with more information about their wages compared with others. Nonunion private-sector employees are more than twice as likely as union employees to say that they are discouraged or prohibited from discussing their pay. Transparency matters.