In Russia, the company's contract with hotels and hostels reportedly does not allow them to offer better rates on competing websites. The FAS says it warned the company about the practice on November 12th, but it didn't respond. We've reached out to Booking.com for comment and more information, and we'll update this article when we hear back.

According to Reuters, if the FAS finds that Booking.com broke Russia's anti-monopoly laws, the company could be forced to pay as much as 15 percent of any revenue it makes in the country as part of a fine. The investigation comes one week after Booking.com agreed with the European Commission to change how it markets discounts on its website. If Booking.com is subsequently forced to change how it does business in the country, it wouldn't be the first US company that has had to do that. In 2017, Google had to start giving Russian Android users the option to pick Yandex as their default search engine when setting up a new phone.

Update 12/31 9:08AM ET: A spokesperson for Booking.com defended the company's business model, saying it gives consumers a "transparent and consistent price comparison experience." You can read the full statement below.