(Opinion only here)
After just posting about how it would be illegal for public officials to use their powers to target lawful entities, it's a bit awkward to almost be arguing the opposite.
Treasury's objection is legitimate. Yes, it was raised in a heightened political climate -- where government lawyers were undoubtedly under pressure to find a legal way to achieve a targeted political goal -- but, they did, legitimately find an articulation that distinguishes abusive inversions from "acceptable" ones. In general, regulators can, and do, disallow specific transactions and articulate new immediate rules that affect already-announced deals (even already closed ones), to stop abusive practices that are clearly beyond the intended scope of the legal framework. (Long time followers of this thread would remember a very similar situation with AbbVie failed acquisition of Shire. Old Allergan was trying to buy Shire to bulk up in defense against Valeant. AbbVie outbid Allergan and signed a deal whose value creation was entirely through inversion. Pyott, a renown skeptic of inversions, despite the intense pressure to make a deal, would not overbid and allowed AbbVie to "win" the bidding. Treasury then changed the inversion rules in midstream, and the deal immediately cratered -- one of the many instances during the takeover battle where the steeled discipline of the old Allergan board dodged a bullet).
An underlying principle of (any) tax code is that transactions whose sole purpose is to reduce taxes may be consummated, but, for tax purposes, it's as if they never happened. (This is not just regarding mergers, but anywhere in the tax code. If you and your employer agree that they will give half your salary to you and the other half to your stay-at-home girlfriend/boyfriend, allowing you to lower your tax bracket [and assuming you are open about it]; the taxman won't stop the deal, but they will tell you to keep paying taxes as if the deal never happened).
Suppose BMW were to buy a small US glass factory, that factory will become (part of) a foreign corporation, no longer subject to US worldwide taxation. It would be unrealistic for Treasury to try to discern if the purpose of the transaction is just gaming tax rules or if BMW really needs a US glass factory. So, unless this deal is entirely devoid of non-tax purposes, it will not be questioned. However, if a pushcart apple vendor in Timbuktu were to buy GE (with the latter re-domiciling to scenic Mali); there would be little question that the deal is intended to abuse the tax code. Treasury won't block the deal, they would simply say that as far as tax rules are concerned, GE is still an American company, and the pushcart vendor is owned by GE, not the other way around. So, the obvious question, to those who always want to be on the edge (and, in competitive environment, if you are not on the edge, you might be uncompetitive), what's the break point between a deal that would be acceptable and one which would be ruled abusive?
Long ago, the policy was that the IRS doesn't make rulings on hypothetical situations. You sign your deal, you close the transaction, you integrate the companies, you file your taxes, you get audited, and then the IRS comes back and say that they disagree with your tax treatment, they might even push criminal charges if they think your claims are too aggressive. It was "do first, we'll tell you if it's legal later." Obviously, that wasn't compatible with a modern global economy in which even the simplest deals can have major tax complexities where reasonable people can disagree. So, over the past few decades, the IRS and Treasury moved toward a more predictable stance. If you present a contemplated deal, they will gladly tell you how they plan to rule on it and give you written guarantees that they won't change their mind later. If you are engineering a deal and want to know their parameters, they'll try to be as open as possible regarding what they consider allowable and what's abusive.
The various inversion percentages that they publish, or other rules and details, are not cast in stone. What is cast in stone is the overarching rule of discerning transaction with a business purpose from sham tax abuses. Treasury, if they feel a threshold or a mechanism is abused, can change it, even retroactively -- even after a transaction closed (unless, of course, they gave you that written guarantee; which is why a standard checkbox item in every deal nowadays is to get that IRS guarantee).
The percentage rules have set a limit where the buyer has to be at least comparable in size to the acquisition. If not, then, as far as the IRS is concerned, the much bigger entity is the one buying the smaller one. Smart accountants and attorneys may find ways to game a bit around rules and parameters; but if anyone thinks that they found a clever way to get a pushcart vendor to buy GE, Treasury has news for them: "NO." (Whatever cute loophole they think they may have found). If necessary, Treasury will rewrite the rules to block that loophole; even retroactively.
One such loophole might be for the pushcart vendor to buy an equal-sized US company (thus meeting the inversion rules threshold) and double in size. Then, immediately afterward, buy another US company that is equal to their new (recently doubled) size, and thus double again. They can keep doubling at a rapid pace until, you guessed it, they are big enough to buy GE. Now, any loophole that allows a Timbuktu apple cart vendor to swallow GE is some loophole!! (just for clarity, these are all tax-purposed transaction, as far as actual ownership and control, it would be GE pulling the strings all along; with the pushcart vendor just a puppet).
This is basically what Treasury is saying this transaction is all about -- a tiny pushcart vendor, doubling through an inversion every few months, trying to buy Pfizer. So, they are not saying you can't do it; they are just saying that, for tax purposes, it will be Pfizer buying Allergan, not the other way around. And, for future reference, they are letting everyone know that if you buy an American company, you can't count the size of that American company as part of the "foreign" portion of the next transaction for another 3 years. You can still play this doubling game, if you want to, but you are slowed to doubling every 3 years (which is plenty fast enough if your transactions have legitimate business purposes; but not if you are a pushcart vendor trying to buy GE).
Having defended Treasury conduct in this situation, I'll be remiss if I didn't add that their conduct is in trying to sustain and defend an unsustainable and indefensible disconnect in US tax laws (where the US is the only country that taxes the worldwide profits of domestic corporations -- thus creating a distinctive disadvantage to being US domiciled). Longtime readers of this thread know that, all along, and with a multitude of actual and contemplated transactions, I've maintained my dual hostility to the tax rules that encourage inversions and to the inversions that are instigated by those rules. Blocking this transaction or that mechanism doesn't solve the problem; only (very temporarily) slows and redirects the outflow path. Unless the US finds a way to harmonize it's tax laws with the rest of the world, one way or another, substantially all remaining major US multinationals will expatriate within a very few years. Rather than going in that direction, the policy winds are blowing in the directions of blocking individual deals and mechanisms rather than harmonizing the tax laws that are nurturing these deals. No dam can indefinitely contain major corporations in a tax-disadvantageous domicile; and sticking fingers into the many leaks the existing dyke has sprouted won't work very long.
Dan.