HSR Merger Review Calendar Resets After Fifth Circuit Vacatur

On March 19, 2026, the U.S. Court of Appeals for the Fifth Circuit denied a motion by the Federal Trade Commission to stay a district court ruling that had invalidated the agency's 2025 overhaul of the Hart-Scott-Rodino premerger notification form. The denial meant the expanded filing requirements, which had taken effect only weeks earlier in February, were dead on arrival, at least for the moment. The old HSR form, familiar to antitrust practitioners since the late 1970s, was back in service. For the agencies charged with reviewing hundreds of mergers each year, the ruling reset the clock on a regulatory project years in the making.

The vacated rule, first proposed in 2023 and finalized in late 2024, was the most ambitious rewrite of the premerger notification regime since the HSR Act itself was enacted in 1976. The new form would have required filing parties to submit draft transaction documents, narrative descriptions of competitive dynamics, details on prior acquisitions, and disclosures about labor markets and supply-chain relationships. The U.S. Chamber of Commerce and other business groups sued, arguing the rules exceeded the FTC's statutory authority and imposed burdens that Congress never authorized. A federal district court agreed, striking the rule down, and the Fifth Circuit's refusal to stay that ruling left the agencies without their new tool.

Less than a week after the Fifth Circuit's decision, on March 25, 2026, the DOJ Antitrust Division and the FTC issued a joint Request for Information seeking public comment on the future of premerger notification. The RFI, covered extensively by JD Supra, asked stakeholders to weigh in on what information the agencies should collect during the initial waiting period, how the existing form could be streamlined, and whether certain statutory exemptions should be narrowed or repealed. The comment period runs through May 26, 2026, compressing a consequential policy debate into roughly sixty days.

The timing of the RFI matters because it reveals the agencies' strategy. Rather than appeal the Fifth Circuit ruling to the Supreme Court, a path that would have consumed months with uncertain odds, the FTC and DOJ opted to go back to the drawing board with formal rulemaking. The RFI is the first step in that process. What emerges from the comment period will shape a new notice of proposed rulemaking later this year, one calibrated to survive the procedural and substantive challenges that felled the first attempt. For merger lawyers, the open question is whether the agencies learned the right lesson from the litigation: that broader information demands require clearer statutory grounding.

Meanwhile, the HSR machinery did not pause. The premerger notification program logged 203 transactions in March 2026, the highest monthly total since December 2025, according to data reported by JD Supra. The 203 filings landed during a month when GDP growth had slipped to 0.5 percent, a figure that historically correlates with slower dealmaking. The filing volume suggests that deal flow is not waiting for regulatory clarity. Rather, parties are filing under the old form, accepting the familiar burdens, and moving toward the waiting-period clock that the HSR Act guarantees.

For transactions that raise no competitive red flags, the waiting period continues to function as Congress designed. On April 21, 2026, the FTC and DOJ granted early termination of the HSR waiting period for RB Global's acquisition of BigIron, the Rutland Herald reported, clearing the way for the deal to close well before the statutory 30-day clock expired. Similarly, Merck announced on April 24 that the HSR waiting period for its acquisition of Terns Pharmaceuticals had expired, removing the last regulatory precondition to closing. Both transactions illustrate the baseline function of the HSR calendar: file, wait, and if the agencies do not act, close.

Federal courts have struck down the FTC's recent overhaul of the Hart-Scott-Rodino (HSR) premerger notification rules, materially reducing filing burdens for reportable transactions., Akerman LLP analysis published on JD Supra, April 29, 2026

The vacatur also changed the calculus for transactions designed to avoid HSR filing altogether. On March 19, 2026, the same day the Fifth Circuit ruled, Senator Elizabeth Warren and Senator Richard Blumenthal sent a letter to Nvidia CEO Jensen Huang questioning whether the company had structured its acquisition of SchedMD, an open-source workload-management software firm, specifically to avoid triggering the HSR thresholds. The letter, covered by JD Supra, highlights a tension that the rulemaking reboot will have to address: the gap between what the statute requires and what a broader agency reading might capture. If a transaction stays below the size-of-transaction threshold but concentrates market power in ways the agencies care about, the current rules give them limited tools to intervene.

The Warren-Blumenthal letter is not an isolated signal. The agencies are also considering whether to eliminate longstanding exemptions that currently shield whole categories of transactions from HSR review. An analysis published on JD Supra on May 2 noted that the FTC and DOJ have signaled interest in narrowing or repealing the exemption for acquisitions of real estate assets, a carveout that has kept most property transactions outside the premerger notification net for decades. The May 26 comment deadline applies to these exemption questions as well, meaning stakeholders in industries from healthcare real estate to data-center infrastructure have a compressed window to make their case.

The broader appellate map shapes how aggressively the agencies can move. The district court ruling that vacated the expanded HSR form was issued in the Fifth Circuit, a jurisdiction not known for deference to agency rulemaking. Any new rule the FTC and DOJ promulgate will almost certainly be challenged in the same forum. That means the agencies must draft the next iteration with an eye toward surviving arbitrary-and-capricious review under the Administrative Procedure Act, the standard that proved fatal to the expanded form. The Fifth Circuit's decision not to stay the district court ruling, while not a final judgment on the merits, signaled that at least two judges on that panel viewed the agencies' position as unlikely to prevail.

What Practitioners Are Watching

For deal lawyers and in-house antitrust counsel, the immediate practical question after the vacatur was straightforward: what form do we file? The answer, following the Fifth Circuit ruling, was the old form. But that simplicity conceals a more consequential strategic question about timing. If a deal is filed in May 2026 under the old form and the agencies subsequently propose a new rule in June that would expand the filing requirements, does it make sense to accelerate closing calendars to lock in the current, lighter-touch regime? Several major transactions, including Allegiant's proposed acquisition of Sun Country Airlines, have already secured early termination of the HSR waiting period this spring, suggesting that parties with clean deals are moving expeditiously.

The resource question also lingers. The expanded form the agencies tried to implement was designed, in part, to front-load information gathering that currently happens during the second-request phase. Without the expanded form, the agencies are back to issuing second requests, civil investigative demands, and voluntary access letters to fill gaps in their initial review. That process takes time and attorney hours on both sides. The March 2026 filing volume of 203 transactions, coming during a period of sluggish GDP growth, suggests the agencies are managing the load with existing tools, but the strain will increase if deal volume continues to climb in the second quarter.

The May 26 comment deadline is the first checkpoint. After it passes, the agencies will have a record of stakeholder views, and the antitrust bar will have a clearer sense of how aggressive the next rulemaking will be. One camp will argue that the vacatur was a procedural defeat, not a substantive one, and that a properly justified rule with stronger statutory hooks can survive judicial review. Another camp will argue that Congress, not the agencies, should rewrite the HSR thresholds, and that any regulatory expansion beyond the current form will meet the same fate in the Fifth Circuit. Between those positions sits the reality of a divided government unlikely to pass HSR modernization legislation, leaving the agencies as the only actors who can move.

The other variable is the Netflix-Warner Bros. transaction. In February 2026, the DOJ opened an investigation into Netflix's $83 billion acquisition of Warner Bros., a deal that stretches the traditional antitrust framework across both horizontal and vertical theories of harm. Clete Willems, Netflix's chief global affairs officer, described the investigation as "totally ordinary" for a transaction of that size, The Wrap reported. Whether the investigation remains ordinary will test whether the agencies' appetite for deep merger review endures even as their preferred information-collection tool has been vacated.

The HSR calendar in 2026 is thus a study in institutional adaptation. The agencies lost a procedural battle but are rebuilding through the RFI process. The courts have drawn a line around what the statute permits. Dealmakers are filing, waiting periods are expiring, and transactions are closing, all under the old rules while the new ones are being drafted. What happens between now and the next notice of proposed rulemaking, likely in the fall of 2026, will determine whether the HSR form remains the quiet workhorse of American merger enforcement or becomes the site of a recurring legal war that shapes which deals get reviewed and how deeply.