Union Free America
The sad fact is that many unions are infiltrated by organized crime. Not all unions or union officials are corrupt. In fact, the vast majority of union officials, especially at the local level, are probably decent law abiding people.
But unionism is about power and "power corrupts" so there are plenty of examples of union corruption. Keeping your fellow workers aware of them is a good way to influence them against getting involved with a union.
The National Legal and Policy Center does an excellent job of monitoring and reporting on union corruption. They publish a twice-monthly "Union Corruption Update" that is absolutely loaded with examples of union corruption in almost every union. The archive of the "Union Corruption Update" is available online and you can search it by union or state.
This page takes a little navigating. Click on "Organized Labor Accountability Project" and then on "Union Corruption Update" to find the information.
If union corruption is of interest to you, send NLPC an e-mail asking them to send you "Union Corruption Update" on a regular basis.