Bernie Sanders urged U.S. Secretary of the Treasury Jack Lew to block a move by pharmaceutical company Pfizer that would create a major tax evasion. In a letter to the Treasury Department on Friday, Sanders explained why the planned $160 billion merger between Pfizer and Allergan would evade U.S. taxation when the headquarters moved from America to Ireland, where Allergan is based.

The potential for Pfizer's tax inversion, or corporate relocation to a tax haven, has a deadline, as the merger would be created in the second half of 2016, the Wall Street Journal reports.

Sanders' letter showed concern that the U.S. does not set any new precedent for tax loopholes. “Blocking this inversion would not only be sound fiscal policy, it would also act as a strong deterrent to other companies that are contemplating similar scams.”

In his letter, Sanders cited “a recent study from Americans for Tax Fairness” that “estimates that preventing the inversion of Pfizer could save as much as $35 billion in revenue.” The Democratic presidential candidate also pointed out that rival “Republican lawmakers are demanding” less money than this merger is slated to create “for the coming fiscal year.”