Message from the US airlines: pack light or pay up.

United earlier this month announced that free bag check-in will be limited to one per person. Starting May 5, it will charge passengers with domestic nonrefundable economy tickets $25 to check a second bag.

Exempt from the fee are those with Premier status or higher in United's Mileage Plus program or those with Silver status or higher within the Star Alliance. The new charge will be applied to tickets purchased in the future.

In a similar attempt to combat rising fuel prices, Spirit Airlines said that it would double charges for all checked bags: to $10 a bag if reserved, and to $20 without reservations.

Report by David Wilkening