For you in particular, likely some moral precepts? or are you arguing that the deterrent effect of government punishment is the only thing stopping you? I don't really understand the line of argument.

When we give money to private citizens it's not a tax. When we give money to the government, it often is.

So paying a union person isn't a tax, any more than paying anyone else. Everything is government mandated or regulated. Is paying interest to Chase Bank a tax? They're federally chartered, and I can't set up my own bank, I'm forced to use a regulated entity.