"But exclusive dealing also can be anticompetitive in some circumstances. For example, exclusive dealing may allow one manufacturer, in effect, to monopolize efficient distribution services and thereby prevent its rivals from competing effectively. As then-Judge Breyer explained, exclusive dealing can harm consumers by thwarting entry or inhibiting the growth of existing rivals:

'Exclusive dealing arrangements may sometimes be found unreasonable under the antitrust laws because they may place enough outlets, or sources of supply, in the hands of a single firm (or small group of firms) to make it difficult for new, potentially competing firms to penetrate the market. To put the matter more technically, the arrangements may "foreclose" outlets or supplies to potential entrants, thereby raising entry barriers. Higher entry barriers make it easier for existing firms to exploit whatever power they have to raise prices above the competitive level because they have less to fear from potential new entrants.'"

https://www.justice.gov/atr/competition-and-monopoly-single-...