Expedia, Starwood Hotel & Resorts and Marriott International are among online travel sites and major hotel groups accused of conspiring to fix prices for hotel rooms and limiting competition.

In the past few years, U.S. travelers have increasingly begun to treat airline tickets as a commodity. Shoppers scour the Internet with the ultimate goal of finding the lowest price, often checking a myriad of Web sites including supplier sites, online travel agencies (OTAs), metasearch sites and deal sites.