Entiltled to Holiday pay or paid time off as stated in employee handbook?

I am a full time employee at Citigroup (40 hours per week). In the employee handbook it states: "Citi provides 10 paid holidays to eligible employees. Some paid holiday time may be granted as a floating holiday, depending on business heeds. Holidays are paid days off for regular full-time employees. Regular part time employee who work 20 hours or more per week are granted the holiday if it falls on their regularly scheduled workday. My manager also sent out an overiew of our department policies for 2009 which states: Full-time employees who are not regularly scheduled to work on a holiday are eligible for a floating holiday to be taken within 60 days after the accrual.
I work a Thursay - Sunday schedule (10 hours per day). My manager and HR now says I am not eligible for the Monday floating holidays (as I received in the past) due to the above line in the employee handbook which states: Regular part time employees are granted the holiday if it falls on their regualry scheduled workday. They claim since I work a Thurs-Sunday scheudle I am not eligible for the holidays that fall on Monday this year (e.g. Martin Luther King Day, President Day, Memorial Day Independence day, & Labor Day). This was told me verbally and would only effect myself and one other person in the department. Can they change the policy without a written notice to the entire department? And does their policy apply to me when it states it is for regualr part-time employees? What recourse do I have?