The Regulators That Decide Merger Arbitrage: A Global Guide

Every merger arbitrage position eventually comes down to the same question: which regulator has to say yes, and how long will that actually take? This guide covers the major merger arbitrage regulators shaping spreads around the world — what each one reviews, how long it takes, and real examples of each in action.

A signed merger agreement is a starting gun, not a finish line. Before most deals can close, they need clearance from one or more competition authorities, and increasingly from foreign-investment or national-security regulators reviewing who ultimately owns and controls a business, separate from competition concerns.

The spread on a merger arb position is, in large part, a bet on how these processes unfold — not just whether they'll ultimately clear, but how long that takes and what conditions might get attached along the way.

The US runs three genuinely separate review tracks, and a single deal can face all three at once.

Nearly every US deal above a certain size has to file under the Hart-Scott-Rodino Act and clear an initial 30-day waiting period with the FTC and DOJ — the size thresholds are adjusted annually, so the exact dollar cutoff shifts each year. A Second Request, a formal demand for extensive additional documents, reliably adds six months to well over a year, and its impact on spreads is immediate: this single event is the clearest signal that a deal has moved from routine to genuinely contested. The two agencies divide cases by industry, and enforcement posture shifts meaningfully with leadership changes at both.

CFIUS runs on a completely separate track, focused on national security rather than competition. It reviews foreign acquisitions of US businesses, with particular scrutiny on semiconductors, defense, critical infrastructure, and ports. Determinations are confidential and the President holds ultimate block authority. Even an indirect foreign-ownership angle — a sovereign wealth fund holding a stake in one of the acquiring parties, say — can trigger a CFIUS review timeline that runs independent of the deal's main antitrust track.

Then there's the track that trips up the most merger arb investors, because it's easy to assume "regulatory clearance" means antitrust clearance and stop there. Insurance, banking, telecom, utility, and transportation deals often need sign-off from specialized bodies layered on top of ordinary antitrust review — and because insurance regulation runs state-by-state, a deal can clear 51 of 52 required jurisdictions and still face a real, live gate in the one that hasn't signed off.

Bank mergers need approval from banking regulators — the OCC, the Federal Reserve, and often state banking departments — on a separate track from antitrust. Railroad mergers go through the Surface Transportation Board, which runs one of the longest, most heavily litigated review processes of any US regulator, with proceedings that can stretch well over a year once formal review begins. Telecom and satellite deals need FCC approval for license transfers on top of standard clearance.

The European Commission's competition directorate reviews mergers meeting specific revenue thresholds under the EU Merger Regulation — broadly, combined worldwide revenue above roughly €5 billion and EU-specific revenue above roughly €250 million for each party, though the exact test has more nuance than that headline figure suggests. Review runs in two phases: an initial Phase I look (25 working days, extending to 35 if remedies are offered or a Member State requests referral), and — if the Commission has real concerns — a Phase II investigation (90 working days, extendable further, especially with late-stage remedies) that typically ends in either a conditioned clearance or, far less commonly, an outright prohibition. For arb purposes, the key signal is simply whether the Commission opens Phase II — that alone reliably adds months and marks a deal as genuinely contested.

The UK runs its own competition review independently of the EU post-Brexit, through the Competition and Markets Authority, plus a completely separate regime for takeovers of UK-listed companies.

The CMA runs an initial Phase 1 look, escalating to a formal Phase 2 panel investigation if it finds a realistic prospect of a substantial lessening of competition. It has a reputation for particularly thorough scrutiny in technology and digital markets.

Takeovers of UK-listed companies go through an entirely different, faster-moving process under the Takeover Panel and its City Code, with real teeth: a mandatory bid triggers at roughly 30% ownership, an offer generally must complete or lapse within about 60 days, and 90% acceptance lets a bidder squeeze out remaining holders. The Panel is known for unusual speed and procedural discipline compared to most competition regulators.

China's State Administration for Market Regulation reviews deals meeting thresholds tied to combined worldwide and China-specific revenue, running through several sequential phases (pre-acceptance, then a formal Phase I of about 30 days, Phase II of about 90 days, and a possible further 60-day extension) that frequently stretch a contested deal's timeline well beyond a year. SAMR technically allows for "silent approval" — a deal clears by default if no decision is issued within the statutory review period — but in practice this is rare for contested deals or those with a significant US or Western nexus: a common tactic instead is for the regulator to prompt the parties to pull their filing and refile, which resets the clock rather than letting it run out. Broader geopolitical tension has made outcomes for deals with any US nexus meaningfully less predictable in recent years.

Japan mirrors the US model of splitting antitrust and foreign-investment review. The JFTC handles antitrust: an initial Phase I review runs 30 calendar days and clears most routine domestic consolidation; if the JFTC issues a report request, Phase II follows, ending at the later of 120 days from acceptance or 90 days from complete responses. Historically one of the more predictable, business-friendly regulators for domestic deals. FEFTA handles foreign-investment review entirely separately, focused on national security in sensitive sectors including semiconductors, defense, and telecommunications.

Canada runs a similar split to the US and Japan — one regulator for competition, a separate one for foreign investment, each on its own clock.

The Competition Bureau reviews mergers under the Competition Act for a substantial lessening or prevention of competition. Notification is mandatory when both a party-size threshold (combined Canadian assets or revenues above C$400 million) and a transaction-size threshold (target Canadian assets or revenues above C$93 million) are met. The initial waiting period is 30 days; a Supplementary Information Request — Canada's version of a US Second Request — extends that until 30 days after compliance, the same kind of contested-deal signal it is south of the border. The Bureau can also review deals that didn't need to be notified, and can challenge a transaction after closing.

Foreign investment runs through the Investment Canada Act instead, administered primarily by Innovation, Science and Economic Development Canada (ISED), and applies to non-Canadian acquisitions of control of a Canadian business. A "net benefit" review is required pre-closing above enterprise-value thresholds that scale with investor type — roughly C$1.45 billion for WTO investors generally, and a higher roughly C$2.18 billion threshold for investors from countries with a Canadian free-trade agreement (including the US, UK, EU, and Japan), both adjusted annually. Separately, and regardless of size, a national-security review can be triggered for any investment by a non-Canadian investor — including a minority stake — if it could be injurious to national security. Net-benefit clearances often come with undertakings; national-security reviews can result in conditions, blocks, or forced divestitures. Cultural businesses run through a specialized track via Canadian Heritage instead.

Foreign-investment and national-security screens specifically have proliferated and tightened worldwide since roughly 2018-2020 — CFIUS reform in the US, a new EU-wide FDI coordination framework, Canada's expanded national-security powers, and comparable moves in Japan, the UK, and Australia. That's a real part of why this second track matters more for spreads today than it did a decade ago.

A few patterns show up again and again once you're actually tracking a live deal.

"All approvals obtained" doesn't always mean done — a deal can clear every jurisdiction in the world and still be stuck, if a single state-level regulator reopens a previously-granted approval, or if separate litigation, rather than the regulatory process itself, is the actual thing keeping the deal from closing.

The regulatory backdrop is also only half the story. Read what the merger agreement itself allows a party to walk away from — some agreements include a negotiated "Burdensome Condition" carve-out that lets a buyer refuse onerous regulatory demands rather than accept them, a fundamentally different risk profile than a deal where the buyer has no such contractual out.

Precedent is genuinely useful — how a regulator has handled similar deals before is one of the better signals available — but it isn't destiny. Posture shifts with leadership changes and political conditions, so let precedent inform a view rather than replace one.

And regulators rarely move in lockstep with each other. It's common for a deal to sail through antitrust review in most of the world while facing a genuinely uncertain fight in exactly one jurisdiction, often the one with the most direct political or strategic stake in the outcome. A shipping merger requiring a foreign government's national-security-style approval, or a railroad merger under a uniquely slow domestic transportation regulator, can sit at a much wider spread than every other regulatory line item on the deal would suggest on its own.