Limit access to Customer/Party level by Business Unit User has an access

Summary:

One of my customers has an issue related to customer data privacy. They need to limit the visibility of customer/party data (at the party/customer level) by the business unit that a user has access to. For example, if User 1 has access to Business Unit A, this user should only see customers that have accounts/sites assigned to Business Unit A. User 1 should not be able to search or see any customer information that belong to any other BU .

Please advise if it is possible to set up any custom security access or if there are any workarounds to achieve this requirement.