Southwest Airlines will begin charging customers a fee to check bags. It's a significant change for the budget carrier, which built years of advertising campaigns around its policy of letting passengers check up to two bags for free.

The carrier announced Tuesday that it will begin charging certain passengers to check their luggage on flights, a significant shift at the company long prized by consumers for its perks.

Southwest Airlines ( LUV 7.40%) is making a number of moves designed to boost profitability, including abandoning its decades-long practice of not charging for checked bags. Investors cheered the news, sending Southwest shares up 16% at the open and up 8% as of 10 a.m. Eastern.