(Bloomberg) -- The Justice Department’s lawsuit filed Tuesday against Alphabet Inc.’s Google adds more allegations of anticompetitive conduct to the mounting antitrust actions against a technology industry dominated by Google, Amazon.com Inc., Apple Inc. and Meta Platforms Inc.

Lawmakers have accused these companies of acting as “gatekeepers” that use their structural advantages in the online economy to disadvantage competitors and stifle innovation. These four companies are facing or have been the targets of 15 antitrust investigations or complaints from federal and state enforcers challenging fundamental parts of their business models and, in some cases, seeking to unwind key acquisitions. 

Google, Amazon, Apple and Meta have a combined market capitalization of nearly $5 trillion, although their market values have fallen sharply from pandemic-era highs when much of society relied on technology platforms. A fifth company, Microsoft Corp. (now worth $1.8 trillion) was sued by the Justice Department in the 1990s, but hasn’t faced antitrust enforcement action lately outside the Federal Trade Commission’s December case seeking to block its $69 billion acquisition of Activision Blizzard Inc.  

The DOJ complaint filed Tuesday against Google was joined by eight state attorneys general and seeks to break up the company’s advertising technology business. The case represents the Biden administration’s first major case challenging one of these tech giants.

Here’s a list of the active, appealed and settled antitrust cases facing Google, Amazon, Apple and Meta:

(Updates with more details about Tuesday’s DOJ complaint in the fourth paragraph. A previous version corrected Microsoft market capitalization to trillion in third paragraph)

©2023 Bloomberg L.P.