I have been asked if it is permissible to state in our disclosures and then charge this:

"If you withdraw any of the principal before the maturity date, we may impose a penalty of 90 days of interest."

If so, I would assume there is some type of document we would get the customer to sign?

Thanks,
Lisa

You would put that in your TISA disclosure when the account is opened/renewed. Customer signs the time deposit agreement or accepts renewal which gives you their acceptance of that withdrawal penalty.