Labor unions are monopolized labor and by definition should be illegal.
Actually that's as bad as forcing someone to join a union in order to work. Both involve the heavy hand of government. Only public unions should be made illegal. Public “servants” should not be permitted to unionize against The People.
MrB wrote with much wisdom on the issue. Eliminate government/union collusion, and most of the unions will dry up on their own. Those that actually serve their employees and produce good results will survive. In a free society, what business is it of you or I to tell someone that cannot voluntarily associate with others to try and better their pay and benefits?