How Mergers Get Their Antitrust Review

U.S. merger review runs on the Hart-Scott-Rodino framework: deals above a size-of-transaction threshold — $126.4 million in 2025, adjusted annually — must be notified to the Federal Trade Commission and the Justice Department's Antitrust Division and wait 30 days before closing. That initial waiting period ends with clearance for the large majority of notified deals. The exception is the second request: a demand for documents and data that extends the review by many months, and marks the deal as one the agencies are prepared to litigate. In the 2020s the agencies' merger challenges reached multi-decade highs before the 2025 leadership change reoriented enforcement toward what the returning administration called clarity and speed.

The Daily News 24 publishes information, not legal advice. This explainer covers a regulatory process.

What are the agencies looking for?

Under Section 7 of the Clayton Act, the test is whether the merger may substantially lessen competition. The agencies' 2023 merger guidelines — the framework documents that structure their analysis — lay out theories: horizontal overlaps where combined share and concentration thresholds trigger concern, vertical integration that could foreclose rivals, potential-competition and serial-acquisition theories, and monopsony harm to workers or suppliers. Market definition is the battleground: the narrower the relevant market, the bigger the combined share looks, and the parties' own documents — strategic plans calling a rival a constraint — routinely decide it.

What is a second request like?

A civil investigative demand for broad document production: custodial emails, strategy decks, pricing data, often millions of pages, produced over six to twelve months with negotiated extensions. The clock matters — merger agreements carry outside dates, and a review that outruns them lets either side walk. Parties can litigate the timing, negotiate remedies, or abandon: the agencies count abandoned deals alongside blocked ones as enforcement wins. The 2023 rule extending the initial review to cover all documents before filing, and 2024 changes to the HSR form's data requirements, lengthened front-end preparation materially.

What remedies settle cases?

Divestiture — selling the overlapping business to a buyer the agencies approve — is the classic fix, and its record is mixed: buyers of divested assets have historically failed to compete about half the time, per retrospective studies the FTC itself cites, which is why the agencies grew skeptical of behavioral remedies and weak divestiture buyers. Conduct remedies — firewalls, nondiscrimination commitments — were disfavored in the 2021–2025 period as policing nightmares. The practical consequence for merger parties: the remedy that clears is the one that removes the overlap entirely.

How did enforcement change in 2025?

The administration change brought new leadership at both agencies and a stated shift from structural presumptions toward case-by-case speed, with the 2023 guidelines surviving but applied with different priorities; a 2025 executive directive on competition policy emphasized quick resolution of genuine cases. Early actions were read as friendlier to vertical and efficiency-heavy deals while retaining willingness to litigate horizontal overlaps. The durable fact across administrations: the HSR process itself — notify, wait, and either clear, extend, or litigate — has run identically since 1978.

What should readers watch in a merger announcement?

The HSR filing and its timing in the deal's 8-K; any second-request disclosure, which resets expectations to a year; the merging parties' market definitions in their public statements versus their internal strategy documents if litigation comes; and the remedy structure if one is proposed. Deal spreads in the market price all of this continuously — the merger arbitrage IS the probability assessment.