The bill targets Alphabet's Google and Meta's Facebook, as well as Amazon.com and Apple, according to Senator Mike Lee's office.
The bill would prohibit big digital advertising companies, with Google the biggest, from owning more than one part of the stack of services that connect advertisers with companies with space for advertisements.
The bill would only impact companies that do more than $20 billion in digital ad transactions. Affected companies would have to do more than $20 billion in digital ad transactions.
"If enacted into law, this bill would most likely require Google and Facebook to divest significant portions of their advertising businesses-business units that account for or facilitate a large portion of their ad revenue," Lee's office said in the statement.
"Amazon may also have to make divestments, and the bill will impact Apple's accelerating entry into third-party ads."
The companies did not immediately comment.
The bill's chief sponsors include antitrust experts including Senators Mike Lee, a Republican, and Amy Klobuchar, a Democrat. It also includes Democratic Senator Elizabeth Warren and Republican tech skeptics such as Senators Josh Hawley and John Kennedy.
In the last legislative session, Congress passed bills to give enforcers bigger budgets and strengthen state attorneys general but legislation aimed at reining in big tech died.
(Reporting by Diane Bartz; Editing by Andrew Heavens)
