This sounds like a job for Xe (Blackwater International) Corporation. The businessmen being targeted have more than enough resources to rent a company of riot control personnel from Xe, as well as intelligence information as to when and where SEIU is planning to attack.
Within a few minutes, a hundred equipped Xe personnel would arrive on scene to insure that the union thugs remain on public property. They may even bring with them noise cancellation equipment that to a great extent would neutralize bullhorns and other noisemakers.
That would be great, especially since the police in that area seem incapable of doing their duty. They should be ashamed, and their boss should be fired.