Quick answer
The airline may require the bag to be checked into the hold and may charge a fee, depending on its policy and your fare.
What to know
If a bag exceeds the allowance, airline staff may ask you to place it in a sizer, pay for an upgrade or gate-check it. Charges and handling vary by airline, route and fare, so check the airline's current policy before travel.
Evidence and review
03_Policies / 02_Baggage_Rules
Reviewed: Review pending