There has been another tax inversion.

Earlier this morning, AbbVie, which is based in Illinois, announced a deal to acquire Ireland-based Shire in a $53 billion deal that will allow the drugmaker to move its tax base to Jersey, an island in the English Channel.

A "tax inversion" is a deal in which a company, say one based in the U.S., acquires another based in Ireland and moves its tax base to pay a lower corporate tax rate. U.S. lawmakers don't like this, because they no longer get a company's tax revenue.

In 2013, AbbVie's income tax expense was $1.2 billion.

The AbbVie-Shire deal is the latest in a series of moves by companies in the pharmaceutical industry to shift their corporate domiciles to enjoy more favorable tax treatments.

Earlier this week, Mylan announced a deal to acquire Abbott Laboratories' non-U.S. developed generic drugs business in a $5.3 billion all-stock deal. The deal involves the creation of a new public company that will be domiciled in the Netherlands, and Mylan said it expects the new company's tax rate to fall into the high-teens within its first couple years.

Last month, Minnesota-based medical-device maker Medtronic acquired Covidien in a $42.9 billion cash and stock deal that will allow the company to move its tax base to Ireland.

Earlier this spring, AstraZeneca rejected Pfizer's takeover efforts, as Pfizer had sought to shift its tax base to the U.K., where AstraZeneca is based.

And Valeant, which has been seeking to acquire Allergan in the most controversial M&A deal this spring, was once the beneficiary of a tax inversion deal, shifting its tax base to Canada from the U.S. with its 2010 acquisition of Biovail.

On Monday, Mylan CEO Heather Bresch appeared on CNBC following announcement of its deal to acquire Abbott's generics unit, and her appearance resulted in a kind of weird conversation about the issue of the tax inversion and Bresch's emphasis on the "strategic rationale" for the deal.

Bresch told CNBC's Bill Griffeth, however, that the company would have "absolutely" done the deal without the tax inversion benefits.

A New York Times report earlier this week said Treasury Secretary Jack Lew sent letters to members of Congress urging action to stop the rush of companies that have shifted their tax base abroad.

And an April report from Reuters said that since 2008, two dozen U.S. companies have moved their legal base abroad as part of a merger, the same number that did so over the previous 25 years.

But analysts aren't holding their breath on a change in the laws.

In a note to investors late last month, Marc Goodman at UBS highlighted some of the firm's top picks in the pharmaceutical space ahead of second quarter earnings. Names included Jazz Pharmaceuticals, Endo Pharmaceuticals, Mallinckrodt, and Perrigo.

Where do you think these companies are based?



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