If you have an employer employee handbook for your job, read it, its term will typically control the issues between you and the employer about promised versus accrued and earned vacation time.If you actually earn vacation time based upon the amount of days per month you work for your employer, the employer cannot take away earned vacation time from you. If there has always been a policy at work of using the earned vacation time or losing it, then the policy is valid and you actually can lose earned vacation time by not using it with the stated time period.Your employer can decrease the amount of vacation promised you initially if the vacation time has yet to be earned. Your option is to either accept the new guidelines and policy as to vacation time with your employer or look for another position with a different company.