One would expect Poland to be wary of socialist "unions" after their post-WWII experience. I like it when the Poles decide to draw the line.
I don't think Poland has to be worried about being invaded by any cheap labor. Poland is where most companies in Western Europe (esp. France and Germany) get their cheap migrant workers from.
The Pole fought themselves out of the communist crap and understood who the real friends are. The EU, oh well...