The US Federal Trade Commission is investigating whether Amazon.com and Alphabet's Google misled advertisers that place ads on their websites, a source familiar with the matter said Friday.

The investigations are being conducted by the FTC's consumer protection unit, and focus on whether Amazon and Alphabet properly disclosed terms and pricing for ads.

Alphabet and Amazon did not immediately respond to Reuters requests' for comments.

The agency is seeking details about Amazon's advertising auctions and whether it disclosed "reserve pricing" for some search ads, according to the source. Reserve pricing refers to the minimum price advertisers must accept before they can buy an ad.

The FTC is also examining Google's practices, including its internal pricing process and whether it increased the cost of ads in ways that were not disclosed to advertisers, the source said.

Bloomberg News first reported the development.