Changes Ahead for Rails and Air
"Under an interpretation of the Railway Labor Act dating to 1934, aviation and rail workers who don't vote on whether to create a union are counted as 'no' votes. That means a union cannot be approved without a full majority of all employees voting yes.
Under the National Labor Relations Act governing other industries, a union can be created as long as a majority of all votes cast are in favor of collective bargaining. In such elections, nonvotes don't count."