Facing a Republican administration with Trump as the President-elect, labor unions are considering the changes in legislation that may occur. With Trump likely to choose a Supreme Court justice, as well as the board members for the NLRB, court rulings and approved labor legislation are likely to be more supportive of employers. Trump could also reverse the Obama administration’s new executive orders concerning labor, including those supporting unions. In the past, Trump has supported right-to-work laws under which employees do not have to pay union dues. According to labor unions, this type of legislation impinges on the functionality of unions.
See "Unions brace for pro-business shift in labor policy under Trump", Timothy Aeppel and Daniel Weissner, Reuters, November 10, 2016