Would you consider this state sponsored slavery?

Because of budget issues in California, correctional officers in the prisons are being forced to take 2 “furlow” days a month. Problem is, they still need to cover the positions for safety sake so they are being forced to work without pay 2 days a month. They say that after the furlow (expected to last 18 months) they will be allowed to take comp days at the discretion of their supervisors. The days must be taken within 2 years or they loose them. With the entire workforce entitled to 36 days it will be impossible to grant all the furlow requests in two years so the people with the lowest seniority will not be reimbursed in part or maybe completely for the time they worked for free. These Correctional officers are supposed to have the most powerful union in the state but they can’t seem to stop this forced slavery. If they strike or don’t show up they can go to jail.
Is this slavery, to force people to work for free?