Aug 6 (Reuters) - Elon Musk's social media platform X on

Tuesday sued a global advertising alliance and several major

companies, including Mars and CVS Health ( CVS ), accusing them of

unlawfully conspiring to boycott the site and causing it to lose

revenue.

X filed the lawsuit in federal court in Texas against the

World Federation of Advertisers, Unilever ( UL ) and Danish

renewable energy company Orsted, in addition to Mars and CVS

Health ( CVS ).

The lawsuit said advertisers, acting through a World

Federation of Advertisers initiative called Global Alliance for

Responsible Media, collectively withheld "billions of dollars in

advertising revenue" from X, previously known as Twitter.

It said they acted against their own economic self interests

in a conspiracy against the platform that violated U.S.

antitrust law.

The World Advertising Federation, Unilever ( UL ), Mars, CVS Health ( CVS )

and Orsted did not immediately respond to requests for comment.

In a statement on Tuesday about the lawsuit, X's chief

executive Linda Yaccarino said "people are hurt when the

marketplace of ideas is constricted. No small group of people

should monopolize what gets monetized."

Ad revenue at X slumped for months after Musk bought the

company in 2022. Brands had been wary of rapid changes initiated

under Musk's ownership.

The advertising group launched the responsible media

initiative in 2019 to "help the industry address the challenge

of illegal or harmful content on digital media platforms and its

monetization via advertising."

X said in its lawsuit that it has applied brand-safety

standards that are comparable to those of its competitors and

that "meet or exceed" measures specified by the Global Alliance

for Responsible Media.

The lawsuit said X has become a "less effective competitor"

in the sale of digital advertising.

X is seeking unspecified damages and a court order against

any continued efforts to conspire to withhold ad dollars.