Hippies and union thugs are about as close to commies as you could get to deal with, so you've got your work cut out for ya (if they take union propaganda as gospel but President Bush is a liar).
Someone should ask your dad what his union dues are buying in the way of politics lately (since about all unions are just another $$$ wing of the DNC). You could also ask if he enjoys working for Howard Dean.
Perhaps that may be a bit too 'in your face' for your parents, but the situation certainly calls for making DUmocrats look like fools (which they are fully capable of doing all by themselves). Your folks could certainly use a history lesson:
I don't think he wants to call his dad a union thug.
Simple enough to say that people vote their wallet and with a parent needing a union for their wages, you know they have to marry the leftist ideals that unions stand behind.
Follow the $$$$$$$$$$$$$$$$$$$$$$$$.
That is why IMO it doesn't matter what argument Justin makes to the parents, bottom like is the $$$$$$$$$$$$$$$$ is directly connected to their political point of view.