The White House declined to comment on Pfizer's deal, but a spokesman told reporters in a briefing that Congress should take action to prevent more such transactions.
The U.S. Treasury Department last week unveiled new rules to clamp down on inversions, its second attempt to do so since a wave of deals peaked in September 2014. But the latest rules amounted to tweaks of existing law and will not impede the Pfizer-Allergan transaction, tax experts said.
03:14 Pew Research study shows 40% of Americans surveyed approve of Trump's Cabinet picks15
22:33 Congress passes 21st Century Cures Act, boosting research and easing drug approvals12
10:11 The 5 Easiest and 5 Most Difficult Promises for Donald Trump to Keep15
20:05 Headphone deal of the day: Klipsch Reference On-Ear Premium headphone for $3014