How long have you been at the store? I believe after six months of employment you're eligible to apply for transfer. Other than that, and this is speculation, I don't believe your store manager is obligated to keep you employed if you have changed your availability outside of the needs of the store. To answer your question more directly, I also don't think it costs your SM anything to keep you on the books and give you zero labor hours, but i'm again not 100% sure.
There are starbucks employee hotlines you can call anonymously for more information, the numbers should be listed in that big notebook that should be near your store's DCR.