Dr. Donald Berwick should not be the head of the Center for Medicare and Medicaid Services (CMS), a group of 42 senators has told President Obama.

Sens. Mike Enzi, R-Wyo., and Orrin Hatch, R-Utah, led the effort to draft the letter, and 40 other Republicans signed it.

In confirmed as CMS director, Berwick will be in charge of many of the activities involved with implementing the Affordable Care Act, the legislative package that includes the Patient Protection and Affordable Care Act (PPACA).

In the past, Berwick has praised the United Kingdom’s single-payer health coverage system, and many Republicans have argued that Berwick is too partisan to be head of CMS.

“The president should start with a clean slate and send the Senate a nominee who is willing to answer our questions and seek our bipartisan support as he or she leads CMS in implementing the new health care law,” Enzi says in a statement about Berwick.

No Democrats signed the letter, and the initial list of signers appears to be missing a number of moderate Republican senators, including Scott Brown of Massachusetts, Susan Collins of Maine and Olympia Snowe of Maine.

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CORRECTION: An earlier version of this article described the initial number of signers of the letter incorrectly. The number of initial signers is 42.