Does an accountant own the QuickBooks data file they prepared and has never been maintained by the client?

Client is leaving the firm and demanding we turn over a back-up copy of their full QuickBooks file that was generated by our office to complete their tax returns. We have never been asked or turned over QB's data files in the past; Client is threatening legal action stating the data file is their Client Records they are legally entitled to receive. We've already turned over hard copies of all necessary records for Client to transition to new accountant.