Regulation CC would only apply to the account holder, who is the tax preparer. In the situation you have described, where customers have signed an agreement stating that they cannot make withdrawals or deposits, the customers would not be considered account holders.

The disclosure requirements and other rules in Regulation CC apply only to “customers”—a person with a bank “account” (12 CFR  229.2(tt)). Regulation CC defines “account” as a deposit that is a transaction account, generally including “accounts at a bank from which the account holder is permitted to make transfers or withdrawals.” 12 CFR  229.2(a)(1). The Regulation CC definition of “account” also specifically includes demand deposit accounts, NOW accounts, ATS accounts, and all of the transaction accounts referenced in 12 CFR 204.2(e). Id. Therefore, if a customer cannot make any transfers (payments to third parties) or withdrawals (payments directly to the depositor), the escrow account is not an “account” for purposes of Regulation CC’s disclosure and other rules.