What you are saying seems closer to “abuse of dominant position”, which is the cornerstone in EU antitrust law, but not so clear in US law where the bar to prove abuse is higher. This does not require a monopoly, just a market share large enough to steer the market. It’s hard to allege this when a company has a minority market share, though.

Yes there is, so I remembered fine on that count. Here is the article I read.

https://www.justice.gov/archives/atr/competition-and-monopol...

Where I was off a little was in mixing market power and monopoly power. As the article explains and corrects my statement to a degree, courts have found it difficult to assign monopoly power when market share is below 50%. However, it does seem possible that a monopoly power can still exist without historical levels of market share. I believe the historical cases do not necessarily apply to technology companies, because these companies throw their power around and enforce it via software and not materialized objects like railroads or commodities. I think being overly preferential to market share is a mistake, particularly for global companies where the market share will vary drastically. In addition, these technology markets are massive. Abuses and competition stiflingly can be very disruptive. They are also very easy to hide behind the complexities of software.

> Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors.

[1] https://www.ftc.gov/advice-guidance/competition-guidance/gui...