Insurers argue that launching these tools would be a costly endeavor that would provide data that confuses consumers. The pharmacy association is directly challenging a part of the rule that would require its pharmacy benefit manager members to report the historical pricing data on prescription drugs. The group said it was not challenging other transparency tenets in the rule.

"These parts of the Trump administration's transparency rule will drive prescription drug costs higher," the association said. "By requiring disclosure of 'historical' net prices, which are essentially current-year net prescription drug prices, the rule will directly provide drug manufacturers access to their competitors' negotiated rebates, discounts and price concessions. This in turn will allow drug manufacturers to discount less deeply as they realize their price concessions went beyond those of competitors."

The chamber's lawsuit challenges provisions that require pricing data to be made available in a massive, machine-readable file to allow third parties to develop shopping tools for consumers.

"These provisions of the rule threaten to reduce competition, and ultimately raise costs to consumers, by revealing confidential, commercially sensitive information that competitors currently do not share with each other," the chamber said in its lawsuit. "The required public disclosure of that closely guarded information runs afoul of long-established protections against the forced disclosure of confidential commercial information, including trade secrets, and is detrimental to the business community as a whole."

Seema Verma, administer of Medicare & Medicaid Services, disagrees with the premises of both lawsuits.

"People are asking for price transparency," she said. "People are frustrated, and that's why we're hearing calls for Medicare for all. Let's just put it out there. Let patients determine what they need and give them the ability to shop around."

Read more: 

• CMS eyes stiffer penalties for price transparency noncompliance
• When it comes to health care services, consumers are missing out on big savings
• Consumers are willing to shop around for a more transparent health care experience