A day after the Obama administration limited the ability of U.S. companies to do international deals to lighten their tax burdens, Pfizer Inc. and Allergan PLC terminated their planned $150 billion merger and other companies around the globe raced to assess the impact of the new rules.

The new Treasury Department rules—the third such attempt to rein in a spate of so-called tax-inversion deals—drew swift condemnation from Allergan Chief Executive Brent Saunders, who criticized them as “un-American” and “capricious.”

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