James Dennin, Kapitall: Last Tuesday alone saw the announcement of $74 billion in potential healthcare and pharmaceutical mergers. In one day. Corporate inversion is the practice of buying another company so that you can relocate. Typically, inversion involves a larger "parent" company and a smaller acquisition target located somewhere with low corporate taxes, like Ireland. Read more from Kapitall: Celebrate International Workers’ Day with these profitable, employee friendly companies That's because American companies are required to have at least 30% of their assets located overseas before they can be considered "headquartered there." When you buy an entire company, that threshold is usually pretty easy to hit, and you also get to benefit from saving on reduced competition and taxes. This is in part what's explaining all of the healthcare merger and acquisition activity that's been going on all year, particularly among drug makers. A lot of the biggest drug manufacturers, like Pfizer (PFE), have seen their costs go up in the last year. Part of it has to do with pressure from insurance companies to provide cheaper drugs. And part of it has to do with expiring patents on major blockbusters like Viagra. That, and the mountains of corporate cash that have been burning a hole in these company's pockets. The pharmaceutical industry has been spending money with particular fervor; a single day last week saw $74 billion in merger activity alone. The latest merger talk in pharmaceutical circles is Pfizer's pursuit of the British drug maker Astra Zeneca (AZN). The latter seems reluctant to be acquired, but Pfizer has been aggressive in its pursuit, despite a long-standing history as one of America's oldest companies. And yet there could also be another reason to account for the huge spike in activity. Congress is in the process of considering raising the amount of assets a US companies needs to maintain overseas from 30% to 50%, making inversion significantly less attractive. Besides, there are only so many attractive acquisition targets located in tax havens anyway. It certainly begs the question of whether pressure will prompt firms into overpaying.