Labor disputes are always contentious, but tying one's adversaries to Nickelback is never an acceptable tactic.

Updated, 4:42 p.m.

Labor contract disputes are messy things, riven with intractable demands on both sides, some reasonable and other unreasonable. Since the current Chicago Teachers Union strike deals with educators' livelihoods, on the one hand, and taxpayer dollars in a cash-strapped city, on the other, tempers are bound to run high.

But I think we can agree that some attacks ought to be off limits -- violence, attacks on the principles' families, and this, via Daniel Strauss:

What must make this sign especially galling for Mayor Rahm Emanuel, the profanity-enhanced former Obama and Clinton aide who took over the Windy City in 2011, is that his taste is actually rather refined: He's more into Wilco, Lucinda Williams, and Laurie Anderson.

In fact, Emanuel's office told RedEye on Tuesday afternoon that the mayor does not like Nickelback.