The lazy union workers in question can't be forced to return to work. They can be ordered to cease a srike/lockout and resume the status quo. If they refuse to return to work, they can then be dismissed for absence.
The lazy union workers choice is to bitch, bitch, bitch and return to the job. It is wise to remember that they get paid for showing up even if they don't have it in their hearts to work.
I could be wrong .. but I'm thinking it was that easy .. they would have fired a lot of workers long ago