CCA and other private prison companies traditionally don't hire unionized corrections officers, which allows them to pay their employees far less than what state employees earn. This is the biggest area of legitimate cost savings offered by privatization, but it often comes at a price (see: everything I've ever written about the quality of guards at private prisons).
CCA is currently facing a challenge from a union in Arizona that represents about 1/3 of the employees at a CCA facility. These officers want half the raise that was just awarded to ICE officers. CCA is offering them 10 cents more per hour, on a salary that already pales in comparison to what governments pay for similar work.
For a much more in-depth analysis of the contract negotiations, go here.