Kroger has to obey the union rule book.  If I'm understanding "calling off" it's when you call in and tell your employer you can't make it in.  You can call in two days but unless you have a doctor's note honoring the third then they can "let you go".  I have worked next to employees for years taking advantage of this to the extreme.  They lasted twenty + years with the company and barely written up.  Then if I went and followed their behavior they slapped the rules heavy on me.  I believe this situation would be called favoritism.  Not sure exactly your situation as there isn't much information.

If you get written up you have to have three before they suspend you.  They have to provide good cause.  You can ask the union to challenge it but I've only found that the union keeps you from being illegally fired.  This is the only company I have had to tell about my disability and use it as a safety guard.  They are more interested in sales than treating their employees like human beings.