Allergan (AGN) confirmed Thursday morning Pfizer (PFE) reached out to the Dublin-based company about combining to create one pharmaceutical behemoth. Lowering its corporate tax burden is a key motivating factor for New York-based Pfizer in any blockbuster deal. As long as the deal is structured correctly, a merger with Dublin-based Allergan would allow Pfizer to 'invert' or take on the lower corporate tax rate available to companies which domicile in Ireland instead of the U.S. Pfizer shareholders would certainly cheer such a move but it would raise some tricky political issues. The U.S. Treasury has already put in place some restrictions to make it harder for U.S. companies to avoid paying taxes by structuring their operations overseas. Drug companies have been the target of sharp criticism of presidential candidates in both parties for drug-price increases, so a high-profile deal between Pfizer and Allergan might bring more negative attention to the pharmaceutical industry. There's a counter-argument, too: Pfizer can't compete with global pharmaceutical companies able to operate with a lower tax burden, therefore something must be done domestically to reduce tax rates for all corporations headquartered in the U.S.