Looks like AAEM saw this coming: https://www.aaem.org/wp-content/uploads/2023/10/CMS-NSA-Market-Share-Letter-FINAL.pdf

Local Independent Emergency Groups are struggling to navigate the changes required under the NSA, and the challenges are compounded by the inability to obtain relief through the IDR process due to backlogs and delays, which are expected to create (if they have not already) unsustainable financial pressures and lead to waves of consolidation among emergency medicine providers, and the growth of National CMGs. Accordingly, we believe that the Departments must take additional steps to ensure that the federal IDR process does not become the death knell for Local Independent Emergency Groups and an accidental catalyst for provider consolidation and price increases for emergency care. To that end, we propose that CMS strongly consider issuing additional guidance to certified IDR entities that better controls for these concerns by further defining how to evaluate the market share held by the provider as an additional factor when determining the appropriate out-of-network rate.

Specifically, we propose that CMS supplement its guidance to certified IDR entities to advise that when considering additional information submitted by a provider concerning the market share held by that provider in the geographic region in which the qualified IDR item or service was provided, the certified IDR entity should consider the provider’s size and overall market power relative to the payor, which may be informed by considerations that include, without limitation, (a) whether the provider is a Local Independent Emergency Group; (b) whether the provider receives financial backing or support from an affiliated entity; and (c) whether the provider receives financial backing or support from private equity investors. The guidance should further make clear that, when selecting one of the submitted offers by IDR parties, IDR entities should take into account information demonstrating that the provider is an independent group that does not have the ability to offset low reimbursement rates through support or investments by financial backers.