vacation time

Can my employer have a use it or lose it policy toward vacation time that has already accrued under CA Labor Code 227.3?

I have worked for the past nine years for a company in California. At the end of 2005, they sent a memo around that stated that from then on, we could only carry forward a week of our vacation. At the end of 2006, I had over two weeks coming. I was actually unable to take vacation because the situation in my department was such that my desk would not be covered if I did so.