I noticed the article that 66 posted is from Fox noise. So to be fair and balanced I will quote from Truthout:
"Restricting unions' collection of dues and forcing them to spend money on things unrelated to effective representation of employees erodes the power of unions and employees and unbalances bargaining power because unions have no significant sources of funds other than dues.
Remember that the NLRA was designed to balance the power of corporations with collective employee power. Given the enormous resources of corporate America, a labor movement with limited resources can scarcely provide such balance. Could that be the goal?"
http://www.truth-out.org/