​Why holiday flying just got Grinchier

Flying over the holidays is never much fun, but this year it may also take a bigger bite from your wallet.

Two airlines are hiking their baggage fees over the holidays, prompting Senator Bill Nelson (D.-Florida) to condemn the practice as appearing to increase airline "profitability on the backs of American families." Nelson is urging the two airlines -- Spirit and Frontier -- to back down from their plans to boost baggage fees for the holidays, and asking other airlines to refrain from joining the higher-fee chorus. Frontier didn't immediately return a request for comment.

Frontier and Spirit are two low-cost airlines known for tacking on fees for everything from baggage to simply receiving an assigned seat. Those extra frills now include traveling with bags over the holidays, with Spirit planning to boost bag fees by an additional $2 from Dec. 16 to Jan. 4, while Frontier will raise bag fees by as much as $10 from Nov. 19 through Jan. 5. That may seem like a small increase, but families who are struggling with stagnant wages aren't likely to be happy to face unexpectedly high baggage fees as they travel over holidays.

"These increased surcharges fly in the face of declining fuel costs and appear focused on increasing profitability on the backs of American families," Nelson wrote in a letter to the CEOs of the biggest U.S. airlines.

Nelson added that a recent report from the Senate Commerce Committee minority staff "found ancillary fees, such as change and cancellation penalties and preferred seating fees, were increasingly keeping consumers in the dark about the true cost of air travel."

Spirit plans to meet with Nelson's office to discuss the issue, a spokesman wrote in an email to CBS MoneyWatch.

Rather than being Grinchy, the airlines are responding to increased demand for checked bags during the holidays, spokesman Paul Berry wrote. "This demand brings added costs for baggage handling, manpower, airport infrastructure, and added weight to aircraft which burns more jet fuel. Every airline must account for this added demand and costs in their prices," Berry added.

Spirit has decreased its fares by 20 percent over the past year, with its average fare now at $68, he noted. The extra $2 baggage fee over the holidays is only for those checking bags, and customers without checked bags aren't charged extra, he said.

Frontier president Barry Bill Biffle told The Los Angeles Times that many businesses raise rates when demand is at its highest, and noted that Frontier's fares are lower than many other airlines. Consumers can also buy a package called "The Works," which is advertised as starting at $49 per person, and includes one checked bag and one carry-on, as well as other "frills" such as the ability to choose your seat assignment.

"We are the best friend for the consumer out there," Biffle told The Times.