Revert of increment

I am working in one engineering college. In our college management has given AP scale to some asst professors with condition of phd in five years. But due to some reason that staff resigned. And now he got letter regarding recovery of increment. But Can icrement given by management been reverted back and recovery be made . 2 : some staff joined college as Technical assistance. But later they acquired qualifications and got promotion Up to asst prof. Now can they be demoted to T.A . Now.