Need Advice on How To Proceed – Partner was Hired in at Full Time only to have it changed with no warning by a Corporate Twit

My (F27) Roommate and Platonic-Partner (NB27) who I will call Sam was hired as a Pharmacy Technician for a rather large grocery-chain to work in their In-store Pharmacies about four or so months ago. When Sam interviewed it was originally for the Part-time position, however the Hiring Manager extended an offer for the Full-time position as the other hiring candidate did not show up to the interview. Since then, Sam has been working full-time hours with the assurance of Full-time Benefits – there were no other part-time or full-time hires after Sam was hired and onboarded.

Enter Corporate Bitch (CB).

Suddenly this lady from Corporate comes in about a month and a half or so ago and claims that Sam is NOT a Full-time Employee and should not be receiving Full-time hours because the store “Needed to cut down on hours”. Sam's manager told CB that Sam was INDEED hired on as a Full-time employee and has been nothing but a champion in making sure Sam gets at the LEAST 32 hours a week. Sam even has the Offer Letter that was accepted and that shows that the position offered was Full-time.

Cut back to today. Sam has just found out that CB not only has made it a big deal on claiming Sam should have been hired in as a Part-time employee and NOT as a Full-time employee, but that CB has ALSO changed Sam's position in the Official Files™ as being a Part-time worker without telling anyone and without Sam agreeing to be Part-time. Sam is now finding out that all of the benefits – Medical, Dental, and Optical – are gone, because “Part-time workers don't have benefits”.

I am absolutely livid and want advice. Is this illegal? I absolutely know that Sam was hired in at Full-time, and we even have the offer letter to back up the claim. What should we do to ensure that:

1. Sam regains her Full-time status as was OFFERED AND ACCEPTED

2. Sam is not fired in retaliation for sticking up for Worker's Rights

3 [Optional]. Corporate Bitch gets some sort of kick in the pants for this underhanded and horrible thing she's done.

More Information: State of Employment is Ohio