It is common for a multi-sector air ticket to have more than one fare basis, particularly if it is for carriage on more than one airline, or different classes of travel are involved. The issuing airline may often have an interline agreement to allow other airlines on the ticket. One disadvantage of this system is that if any change is made, the most restrictive fare rule, and/or the highest change fee, may apply to the entire ticket, not just the portion being changed.[8]