Apple, Google, Amazon and Facebook's CEO's Tim Cook, Sundar Pichai, Jeff Bezos and Mark Zuckerberg respectively, appeared virtually as David Cicilline, a Democrat representative on the House Judiciary Committee's antitrust panel, opened the hearing saying: "Simply put, they have too much power."
He then asked Pichai, the head of Alphabet, Google's owner: "Why does Google steal content from honest businesses?"
Whilst he accused the firm of de-listing Yelp from their search engine
However, denied this to be true and insisted Google operates with the "highest standards".
Zuckerberg, meanwhile, was called out over Facebook's purchase of Instagram in 2012 after claims they bought the the photo-sharing app because it allegedly posed a threat to their business.
However, the CEO insisted that was not the case.
He said: "It was clear that this was a space that we were going to compete in one way or another. I don't view those conversations as a threat in any way."
Elsewhere, Bezos faced claims that companies who sell via Marketplace have described getting their payments from Amazon as like a"drug", because they feel great when they sell products, but the high doesn't last long when the firm sells the same products themselves.
The rep said: "Mr Bezos, this is one of your partners. Why on earth would they compare your company to a drug dealer?"
However, he was adamant that was not true.
He replied: "I completely disagree with that characterisation."
Much more was discussed during the intense grilling.
Cicilline closed the hearing by stating: "This hearing has made one fact clear to me: these companies as they exist today have monopoly power. Some need to be broken up, all need to be properly regulated and held accountable. We need to ensure the antitrust laws first written more than a century ago work in the digital age."
The meeting was actually supposed to be staged at an earlier date, but the coronavirus pandemic derailed those plans.
All four firms face tighter regulation as the US cracks down on the dominance of tech giants.