Google Accused in Suit of Fixing Ad Rates With Facebook Deal

Alphabet Inc.’s Google was accused in an antitrust lawsuit of giving itself the edge in online advertising by cutting a cozy deal with Facebook that gives the social network an advantage in virtual auctions which determine whose ads appear where.

The deal has allowed Google to retain its dominance in online advertising while keeping other advertisers on the sidelines and limiting revenue for online publishers, two Massachusetts companies claimed in a proposed class-action lawsuit.

A so-called header bidding system devised in 2014 enabled publishers to direct a user’s browser to solicit real-time bids from multiple exchanges, not just Google’s, ...