At a minimum, they will investigate this and make inquiries (typically within months) if they see a high volume of complaints.

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

"Some mergers change market dynamics in ways that can lead to higher prices, fewer or lower-quality goods or services, or less innovation.

Section 7 of the Clayton Act prohibits mergers and acquisitions when the effect "may be substantially to lessen competition, or to tend to create a monopoly." "