"the case of Pfizer, it reported an effective tax rate of about 25 percent in its most recent filing. Allergan's is reported to be significantly lower, thanks in part to Ireland's 12.5 percent statutory"

"The threat of Pfizer moving its headquarters outside the U.S. would realize the fears of lawmakers such as newly installed House Speaker Paul Ryan, who has sought to reform the corporate tax code. It also has drawn the ire of Democratic lawmakers..."