I have a unique situation in that I support 5 seperate companies which all sit in the same office space.  The companies are seperated by card key access.  Four of the five companies share common ownership.  Each company has it's own EIN.  If an employee is moving from one company to another, are there legal ramifications to allowing the new manager to see past reviews even though it's a different company?  Also, can I ask the former manager from the old company to do some type of mini review of the employee to provide to the new manager with the new company?  I ask this because we use and HRIS system which houses all the reviews in their database and I need to understand what type of visibility new managers in the different company should have to it.

 Thanks.  Please ask for clarification as I know this scenario sounds rather confusing.

The different EIN shouldn't matter as they are owned by the same entity, meaning there is a central body that has access to all the info anyway.

Strip away the corporation and imagine that Bob owns a hardware store and a lawn care business.  Frank, who works for Bob in the store, quits his store job on good terms and takes a job with the lawn care business.  Since Bob owns both entities, Bob has access to both pieces of information.  This doesn't translate into much more than an inter departmental transfer.  Can you sue Bob for Bob using Bob's own information to make a decision in Bob's own business?

Because the structure you are in sounds a little larger and more complex than the operation I've described, I'd find the Bob in your situation and ask him personally if he cares.  I don't think he should mind at all, particularly because it helps his business.