HSR Act Antitrust Review: Merger Approval Process

Key Takeaways

• HSR Act filings are required for US transactions above $126.4 million (2025 threshold), triggering a mandatory 30-day waiting period.
• A Second Request suspends the clock and typically adds 6–12 months, making it the single biggest source of deal-timing uncertainty.
• A deal that clears HSR in 30 days can still wait a year or more for Chinese SAMR clearance on cross-border transactions.
• Assuming HSR is a formality is the most costly merger-arbitrage mistake; roughly 1 in 4 reviewed deals faces substantive issues.

What It Is

The Hart-Scott-Rodino Antitrust Improvements Act of 1976, codified at 15 U.S.C. § 18a, requires parties to certain large transactions to file a premerger notification with the FTC and DOJ and wait a minimum period before closing. The filing gives the agencies a first look at the deal and, if they see a potential competition problem, time to investigate before the combination becomes final.

Either the FTC or the DOJ takes the lead on a given deal, typically based on industry expertise. The FTC generally handles pharmaceuticals, grocery, and hospitals. The DOJ handles airlines, telecoms, financial services, and technology. The result is the same either way: an agency with power to clear the deal, clear it with conditions, or sue to block it.

The Intuition

Congress passed HSR after decades of post-closing merger lawsuits where the agencies tried to unwind completed deals. Unscrambling a merged company is messy and often impossible. The premerger regime flips the burden. Large deals sit in a mandatory quiet window during which the agencies can study competitive effects, request documents, and negotiate remedies. If no concerns surface, the deal closes. If they do, the parties either agree to divestitures or face litigation.

For investors, HSR timelines matter because they determine when a deal actually closes and when merger arbitrage spreads compress. A clean filing clears in 30 days. A complex one can take a year or more.

How It Works

Filing thresholds. The size-of-transaction test is adjusted annually based on gross national product. For 2025 the threshold is $126.4 million. Transactions above this value generally require a filing. A size-of-person test applies between $126.4 million and $505.8 million, requiring that one party have at least $252.9 million and the other at least $25.3 million in annual sales or total assets. Deals above $505.8 million trigger HSR regardless of the size of the parties.

The filing. Each party files an HSR Form with supporting documents, including strategic materials (so-called 4(c) and 4(d) documents) that discuss competition, market share, and deal rationale. Filing fees scale with transaction size, topping out at $2.39 million for the largest deals in 2025.

Waiting periods. Once both parties file, the statutory 30-day waiting period begins (15 days for a cash tender offer). During this window the parties cannot close. The agencies can grant early termination, though that practice was suspended in 2021 and remains limited.

Second Request. If either agency needs more time, it issues a Second Request for documents and data. This suspends the clock and typically adds six to twelve months while both sides negotiate scope, produce millions of pages, and answer interrogatories. A Second Request signals a substantive concern and is the single biggest cause of deal delay.

Outcomes. After review the agency can (1) close the investigation and let the deal proceed, (2) negotiate a consent decree requiring divestitures or conduct remedies, or (3) sue in federal court to block the deal. Parties can abandon the transaction at any point, often triggering a reverse termination fee.

International parallels. Deals with cross-border activity usually trigger filings in multiple jurisdictions. The European Commission Directorate-General for Competition (DG COMP) reviews deals meeting EU turnover thresholds. The United Kingdom's Competition and Markets Authority (CMA) reviews UK-nexus deals. China's State Administration for Market Regulation (SAMR) has become a frequent gating item on large cross-border transactions. A deal can clear HSR in 30 days and still wait a year for SAMR clearance.

Worked Example

Suppose Acquirer Co. (annual sales $4 billion) announces a $600 million acquisition of Target Co. (annual sales $200 million). Because the deal exceeds the $505.8 million size-of-transaction threshold, HSR applies and the size-of-person test is irrelevant.

Both parties file HSR Forms with a filing fee scaled to the $600 million bracket. The statutory 30-day clock begins on the day both forms are received. On day 25, the FTC issues a Second Request citing overlap in two product lines.

The parties spend nine months negotiating scope, producing documents, and running econometric models. The FTC ultimately agrees to a consent decree requiring divestiture of a plant that serves the overlapping market. Fourteen months after announcement the deal closes. Merger arbitrage spreads that opened at $3 per share narrowed only as the consent decree was finalized.

Common Mistakes

1. Assuming HSR is a formality. Most deals clear without a Second Request, but the ones that do not often close six to eighteen months late or not at all. Treating HSR timing as fixed at 30 days undercosts risk in merger arbitrage and financing plans.

2. Ignoring non-HSR foreign filings. HSR is only the US piece. Deals with EU or UK revenue thresholds hit DG COMP or the CMA independently. China's SAMR reviews can be the slowest leg of a global transaction.

3. Underestimating 4(c) document risk. Internal strategy decks that discuss competitors in language the agency can quote back (for example, "eliminate a rival" or "price to take share") can turn a routine review into a contested case. M&A counsel routinely screen these documents before filing.

4. Confusing HSR clearance with antitrust immunity. Closing after HSR does not immunize a deal from later challenge. Private plaintiffs and state attorneys general can still sue, and the federal agencies can reopen matters based on new evidence.

5. Missing the size-of-person test. Deals just above the size-of-transaction floor and below the upper cutoff need to apply the size-of-person test to either party. Filings are sometimes skipped because one side assumes it is too small, only to discover after closing that a filing was required and civil penalties apply.

Frequently Asked Questions

Q: What is HSR Act antitrust review in simple terms? The Hart-Scott-Rodino Act requires parties to large transactions to file a premerger notification with the FTC and DOJ and wait before closing. It gives federal regulators a mandatory window to review competitive effects before a deal becomes final and potentially irreversible.

Q: How does HSR review affect investment decisions? HSR timing directly determines when a deal closes and when merger-arb spreads compress. A clean filing clears in 30 days; a Second Request can add 6–12 months. Misestimating this timeline is a common and costly mistake for both deal teams and arbitrageurs.

Q: What is a real-world example of HSR review impact? A $600M acquisition above the 2025 threshold receives a Second Request on day 25. Nine months of document production and econometric analysis follow. The deal closes 14 months after announcement, a year past the original 30-day expectation, with a negotiated consent decree requiring a plant divestiture.

Q: How can investors use HSR review in merger-arb analysis? Read the deal announcement for references to horizontal market overlap and the identity of the reviewing agency (FTC or DOJ). Cross-border deals with EU, UK, or Chinese nexus add parallel review timelines that can easily exceed the US process. Price the spread to reflect the longest expected regulatory timeline, not the shortest.

Q: How is HSR clearance different from full antitrust immunity? Clearing HSR only means the agencies chose not to challenge the deal before closing. Post-closing challenges from state attorneys general, private plaintiffs, or federal agencies reopening based on new evidence remain possible. HSR clearance is a green light to close, not a permanent safe harbor from antitrust liability.

Sources

1. Cornell Legal Information Institute. "15 U.S. Code § 18a: Premerger Notification and Waiting Period." https://www.law.cornell.edu/uscode/text/15/18a
2. Federal Trade Commission. "Premerger Notification Program." https://www.ftc.gov/enforcement/premerger-notification-program
3. Federal Trade Commission. "New HSR Thresholds and Filing Fees for 2025." https://www.ftc.gov/enforcement/competition-matters/2025/02/new-hsr-thresholds-filing-fees-2025
4. U.S. Department of Justice Antitrust Division. "Merger Enforcement." https://www.justice.gov/atr/mergers

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.