Tuesday's letter came from House Energy and Commerce Committee Chairman Fred Upton (R-Mich.) and Rep. Cliff Stearns (R-Fla.), who leads the panel's Subcommittee on Oversight and Investigations.
"We write to you today because we believe more information is needed to determine whether QSSI will be able to act effectively in this role in a fair and transparent manner," Upton and Stearns wrote to Health and Human Services Secretary Kathleen Sebelius.
Sen. Orrin Hatch (R-Utah) has also expressed concerns over UnitedHealth Group's purchase of QSSI. Another critic compared the deal to the New York Yankees buying off their umpires in a conversation with The Hill.
A senior executive with Optum, the subsidiary of UnitedHealth Group, which bought QSSI, said his firm and UnitedHealthcare are entirely separate businesses.