That was last month.  http://raycomgroup.worldnow.com/story/31171470/kroger-workers-authorize-strike-in-battle-over-health-care-costs

Yeah, it's true but it only said the employees voted to authorize the strike.  It doesn't mean there is going to be a strike.  I heard old timers here say if there was another strike, Kroger would shut the stores and move somewhere else.  Kroger owns the union or knows how to grease those making decisions for the union.  So, I doubt it would faze Kroger and I doubt the union would really want to strike.   You should have received an email or something in the mail.  Ask your union rep what is up.  Or call the union hall and ask.  You pay dues so should be aware of what is going on.

I wouldn't worry about the slashed tires.  I would be concerned about the Columbia neck tie.  I have heard of guns being pulled on fellow employees.  Another ended up on a meat hook dead but I am not sure if that was during the strike.