Although in many/most cases the depreciation schedules are prepared and maintained by the practitioner, they are considered to be part of the schedules that make the client's books and records complete, and are necessary to fulfill current or future tax obligations. Depreciation schedules are considered client records and not providing it would fall under Sec 501 as an act discreditable to the profession to hostage records. Even if this CPA is not a member of the AICPA, he or she is still held to the state standards and those of Circ 230 and state revenue depts. My state society actually uses the AICPA standards and rules so that even if not a member of the AICPA in this state, we must still abide by the AICPA rules.
The rule you are looking for is Circ 230, sec 10.28 (b ).
Here's an article from the AICPA's publication, The Tax Advisor, from Aug 2014 that covers your issue. http://www.aicpa.org/Publications/TaxAdviser/2014/august/Pages/TPR_Aug14.aspx
Here's another good summary by the Pennsylvania Institute of CPAs: http://www.picpa.org/Content/cpajournal/2006/summer/8.aspx
ETA (again): I see you are in NY. If this CPA is also in NY, here is part of the NY code of professional conduct that says the same thing, that the deprec schedules are part of the client records, and that they must be given to the client: http://www.nysscpa.org/prof_library/ethics/Rules/codeother.htm