when offered position company did not disclose that I would lose vacation time can they now take it?

My department was closing, I was given the options of severance or apply to another department. After accepting the job, a few months later I discovered my vacation time was reduced. I brought it to the attention of my supervisor, who said she didn't know why it changed. She contacted our first level HR Rep and she didn't know why it changed...commented "probably due to transferring to this department" and had to research it with another HR guy, who wasn't aware of it either. The person in charge of our department, today (over 3 months into new position) told me that I am losing a week of vacation and said HR said nothing can be done and severance was no longer available. Had I of known vacation time would of been reduced I would have not accepted the position and taken the severance option. Do I have any legal options here?