ABOARD AIR FORCE ONE (Reuters) - The White House said on Thursday that the best way for the government to fight tax avoidance would be for Congress to take action after the U.S. Treasury Department issued major new rules on tax inversions on Monday. “I know that if they are working on any future actions the most impactful thing we could do is if Congress took some action here,” White House spokesman Eric Schultz told reporters when asked if the Treasury Department would issue more regulations on tax avoidance.  U.S. drug maker Pfizer Inc agreed on Tuesday to terminate its $160 billion agreement to acquire Allergan Plc in a victory for the Obama administration’s push to stop tax-dodging mergers. (Story corrects quote to reflect spokesman saying Congress would have most impact on countering tax avoidance, not that Treasury is working on more action.) 