From a report at the link below:
Republican lawmakers rolled out plans Monday for the first major reform of federal labor laws in six decades, including changes that could deal a potentially crippling blow to union political power if adopted.
Dubbed the Employee Rights Act, the legislation would affirm the individual rights of workers, giving them more options to walk away from unions if they do not feel the organizations are representing their interests.
Labor unions have spent $573 million in elections over the last decade, 90 percent of that aiding Democrats, according to the Center for Responsive Politics. However, exit polls in 2008 and 2012 show that about 40 percent of people covered by union contracts voted Republican. That suggests a substantial portion of members are unhappy and would opt out if they could. That would severely cut into union treasuries, hurting the Democrats who depend on them.
Full report here.