They must return to you any and all records of yours that are necessary for you to comply with your Federal tax obligations. That would include any documents or materials provided to the tax practitioner or obtained by them in the course of representing you. It also includes materials provided to the practitioner by third parties. They also have to return to you any claim for a refund, schedule, affadavit, appraisal, or any other document they prepared "if such document is necessary for the taxpayer to comply with his or her current Federal tax obligations".

Pages 18 and 19 of IRS Circular 230 cover these obligations: http://www.irs.gov/pub/irs-pdf/pcir230.pdf