"Because your company is paid more when it reaches lower payment amounts, the payments to health care providers are often far lower than the billed amount, with some describing these amounts as 'crazy low,'" Wyden and Sanders told Dalton.

The senators asked Dalton to brief their committees on the concerns about Data iSight that were raised by The New York Times, whether or not they believe they are classified as fiduciaries under the Employee Income Security Act and whether they have applied for and been granted a prohibited transaction exemption from the U.S. Labor Department for Data iSight fee revenue.

The New York Times reported on use of the Data iSight repricing tool April 7.

Health insurers and self-insured employer health plans can use the tool to assess the reasonableness of out-of-network providers' bills and then decide whether to pay the claim, negotiate a lower price or pursue another strategy.

Adventist Health System and Community Health Systems are two of the hospital owners that have filed antitrust suits against MultiPlan over the Data iSight system because they believe the payments repriced with help from the Data iSight tool are too low.

The No Surprises Act is now supposed to protect insured patients from big, unexpected medical bills related to emergency care or to the appearance of out-of-network providers at in-network hospitals. But patients can still get "surprise bills" in other circumstances.

Related: Reference-based pricing can keep your benefit costs down

According to press reports, in some cases, employer use of Data iSight to reprice claims "leaves patients with sky-high medical bills that they are on the hook for paying," Wyden and Sanders wrote in their letter.

MultiPlan asserts in a response to the Adventist suit that hospital companies object to the Data iSight system because it keeps hospitals from forcing patients to pay much higher prices for care in some hospitals than they pay for the same care in other hospitals.

"Using antitrust law to stifle competitive innovations and thereby gain an upper hand — all to admittedly inflate profits by forcing patients to pay substantially higher prices for the exact same medical services — is as wrong as it sounds," MultiPlan said.

MultiPlan said in a response to the Wyden-Sanders letter that it helps make the health care system work better by reducing or eliminating medical bills and out-of-pocket costs for millions of patients.

"We are working with the committees to address their questions and explain the cost and complexity patients can face when obtaining out-of-network medical services, especially when many providers charge many times more than what they charge Medicare and commercial in-network patients for the same services," the company said.

"We are committed to helping make health care transparent, fair and affordable for all," the company added.