U.S. multinational corporations have been dodging billions of dollars in taxes by undertaking a corporate inversion. An inversion is when a larger U.S. company buys a smaller foreign company that is usually located in a tax haven. The U.S. company then becomes a subsidiary of the foreign company. This allows it to change its legal address to a foreign country with a low tax rate, even though the entire company continues to be operated from America.

The U.S. Treasury Department has proposed a rule that will deny a major tax break to corporations that undertake an inversion. It’s known as the “serial inverter” rule. It would deny tax breaks to corporations that have done multiple inversions in order to dodge U.S. taxes by changing their legal address to a lower-tax foreign country. Pfizer, which was merging with a serial inverter, lost a $35 billion tax break it was counting on because of Treasury’s proposed rule.

But the Treasury Department needs to feel pressure to make this rule FINAL, and to make it even stronger by applying it to all corporations that invert with a foreign firm. That would take away the ability of corporations that invert from doing a "hopscotch loan," which lets them dodge paying U.S. taxes on the billions in offshore profits they have stashed in tax havens.