Vacation Policy Change

I have been with my employer for 8 years now and our vacation policy has always been that you could carry over 1 1/2 times your accured vaction, and at seperation any unused vaction was paid out at 100%. We have just been advised that as of January 1 our policy is changing and we will be going to a use it or lose it policy. We have the option of letting our current time role over to the new year and risk losing it at the end of 2013 (180 Hrs in my case) or we could have it paid out at only 75% of our hourly rate. Is an employer allowed to pay you only 75% of time earned. With 180 hours in the bank and earning an addtional 160 in 2013 there is no way all of this time off would be approved based on business needs. I don't mind the policy change but do have a problem with getting only 75% of time already earned.