just wondering what to do

Im a night shift CNA at a little nursing home in north central kansas, and we have a new administrator and a LPN wo is due to take her boards in may as a ADON, well the problem is that they have decided to take all 12 hour CNA shifts away an d go to 8 hr while the nurse stay at 12 hour shifts, I've worked there 7 years and probably missed that many days (7) in calling in I like and was hired for twelves, and they never even discused the change at all with any of the noc shift....why can they give my hours that im willing to work to people they havent even hired yet, can they do this and what if anything can we do about keeping our shift???