Americans pay billions in "junk fees" every year. Here are some of the worst.

Lauren Wolfe said she first noticed "resort fees" in 2016 during a vacation in Key West, Florida. She'd paid $400 a night for a hotel room during the peak season, but was stunned when the hotel declined to hand over her room key unless she paid an extra $20 a day to cover a resort fee. 

"It's just a cash grab by the hotel," said Wolfe, a lawyer who was spurred by her experience to start a site called Kill Resort Fees aimed at alerting consumers about the hidden charge and helping them take action. She's also the counsel for Travelers United, an advocacy group for travelers.

In her view, consumers are misled by the fees because they aren't typically disclosed when they book a room. It's difficult to determine the true cost of lodging when all the fees aren't presented up front, she noted.