If pharmacy group Walgreen were to relocate its tax home-base to Switzerland, the United States would lose about US$4 billion ($4.6 billion) in tax revenue over five years, activist groups said on Wednesday.
The largest US pharmacy chain, based in Illinois, is under pressure from some of its shareholders to do a deal known as a tax inversion with Alliance Boots that would shift Walgreen's tax domicile overseas.
Two groups issued a report that said such a move would be seen by many Americans as "deeply unfair and unpatriotic".
"Walgreens should show its commitment to our communities and our country by staying an American company," said Nell Geiser, an official at Change to Win, a labour union coalition. The other group releasing the report was Americans for Tax Fairness, a tax activist group that gets some of its funding from unions.
The two groups, citing estimates from three Wall Street investment firms if Walgreen were to do an inversion, said the move would add up "to more than US$4 billion in lost tax revenues over five years, most of which would likely have been paid in the United States."
Walgreen, which has more than 8000 stores, bought a 45-per cent stake in Swiss-based rival Alliance Boots in 2012, with an option to buy the rest in 2015.
Walgreen spokesman James Graham said: "As we've said before, we continue to analyze a number of issues as we move toward the window for exercising the second step of our transaction with Alliance Boots, and we will do what is in the best long-term interest of our company and its shareholders."
Inversions are still rare transactions, but they are becoming more common. Of roughly 50 such deals done in the past 25 years by US companies, half have occurred since 2008.
Wall Street investment analysts have said that Walgreen could lower its tax bill through an inversion.
Proposals to curb these kinds of deals have been offered in the US Congress and by Democratic President Barack Obama, though policy analysts expect none of them will become law soon.