14 CFR 260.8: Disclosing material restrictions, conditions, or limitations.

In carrying out the requirements of § 260.6(c), a covered carrier must clearly and conspicuously disclose, no later than at the time of voucher or credit offer, any material restrictions, limitations, or conditions on travel credits, vouchers, or other compensation, including but not limited to validity period, advance purchase requirement, capacity restrictions, and blackout dates, regardless of whether consumers are entitled to a refund.