Yesterday, daisyNews shared data on payment denials citing non-membership in Medical Provider Networks (MPNs) and, in multiple cases, showed that the provider was a member of the payer’s MPN.

Payers are denying tens of thousands of bills in this manner. Even worse, providers have no real recourse for pursuing reimbursement.

California's MPN system enables payment abuse, thanks in large part to the failures of the state agency responsible for overseeing it. When a payer improperly denies reimbursement by incorrectly alleging MPN non-membership, the provider has no reliable way to push back.

California regulations don't require payers to identify the MPN they're invoking to deny payment; a payer can cite CARC 242 ("Services not provided by network/primary care providers") without specifying which of their potentially dozens of MPNs the provider supposedly isn’t in. With no MPN name or ID number, the provider must rely on whatever scraps of information the payer provides or use an unreliable state website to determine which MPN is the basis for the denial.

If the provider somehow identifies the right MPN, their only way to dispute the denial is to submit a Second Review appeal with a screenshot of the MPN website’s provider roster. This roster may or may not exist, may require a password, and is subject to update without notice.

If the payer denies the Second Review appeal, it’s the end of the road. The California Division of Workers’ Compensation (CA DWC) has repeatedly declared MPN-based disputes ineligible for Independent Bill Review (IBR). The only remaining option is to hire a lawyer, file a lien, and take the dispute to the Workers' Compensation Appeals Board (WCAB), a potentially lengthy and costly ordeal that few providers would undertake over a single bill.

The predictable result: with no guarantee of payment, providers exit workers' comp, care becomes harder to access, and employers keep paying rising premiums into a system that increasingly fails their injured employees.

EORs Fail to Identify MPNs

Despite our polite suggestions, California regulations do not require payers to specify which MPN they are invoking when denying a bill for MPN non-membership.

As yesterday’s Employers examples show, a payer can claim the provider delivered care out of network without naming the MPN in question. With no actionable information from the payer, the provider can try to turn to the CA DWC’s frequently glitching and/or outdated online MPN list.

This leaves providers dangerously exposed.

As daisyNews has documented, a single payer or employer can maintain dozens of MPNs. Sedgwick, the state's largest Third-Party Administrator, maintains 294 MPNs according to the CA DWC list, of which 38 are currently active. If Sedgwick denies a bill for MPN non-membership, the MPN in question could be any of those 38 (or, realistically, any of the 256 inactive ones).

Some Sedgwick MPNs have obvious ties to specific employers (e.g., Sedgwick/Harbor MPN – Lowes). Many, like those we list below, do not (note: Careworks and WellComp are Sedgwick companies). How can any provider distinguish between these MPNs ?

• Sedgwick Extended Medical Provider Network
• Sedgwick Standard Medical Provider Network
• Sedgwick/Harbor MPN
• Sedgwick/Harbor 3 MPN
• Sedgwick/Harbor 2 MPN
• Sedgwick/Harbor MPN – Transform
• Careworks MPN
• Careworks Advantage Plus MPN
• WellComp MPN
• Sedgwick/Harbor MPN – DTFD
• Sedgwick/Harbor MPN – DESC
• Sedgwick/Harbor MPN – CEC
• Sedgwick/Harbor MPN – AG

Even if a provider has access to their written acknowledgement confirming MPN participation,there's no guarantee it covers the specific MPN cited on the Explanation of Review, or that the MPN hasn't since dropped them from its roster (which state regulations require payers to update only four times annually).

A Screenshot and a Prayer

To appeal an MPN-based denial, a provider must:

1. Call the claims adjuster to identify the applicable MPN and MPN ID number.
2. Locate the website for that MPN's provider roster, which may not exist or be on the CA DWC’s website, and which may be password-protected.
3. Search the roster for their name.
4. If listed, capture a screenshot.
5. Submit the screenshot with a timely Second Review appeal.

The payer or its MPN’s website and provider roster are the only evidence available to contradict the denial.

Even this workaround is fragile. Again, MPNs can add or remove providers at will, and the state requires roster updates only quarterly. A provider confirmed as a member on the date of service can be removed without notice the following week, and only learn of it when a denial arrives. A screenshot captured today may not reflect the roster tomorrow.

IBR: Not an Option

Providers familiar with California's workers' comp payment disputes may assume that if the payer denies the Second Review appeal, there’s always IBR. This is not the case.

IBR adjudicates disputes over the amount of reimbursement owed for treatment. It cannot resolve "threshold" questions (such as liability or provider eligibility) about whether any reimbursement is owed at all.

On multiple occasions, the CA DWC has specifically declared MPN non-membership denials "ineligible" for IBR, giving payers free rein to cite MPN status without fear of the state overturning the denial. As past examples show, this "ineligible" determination applies even when the payer authorized the treatment.

That leaves the WCAB as the sole recourse. While this avenue exists in theory, the cost and time required to pursue a single bill make it wildly impractical. Payers are undoubtedly aware of this.

No Consequences for Payers

The CA DWC does not audit MPN denial patterns, and in our experience, does not act even when presented with hard evidence of systemic payment violations. It does not require payers to substantiate MPN-based denials on EORs, nor penalize payers for denials later found to be incorrect.

Thanks to the CA DWC's years-long violation of state law requiring it to enforce mandatory claims data reporting, no comprehensive claims dataset exists that would allow regulators or employers to identify which payers are abusing CARC 242, or how often. daisyBill's data are the closest thing California has to a representative sample of the problem.

When daisyBill formally petitioned the CA DWC to revoke an MPN, documenting incontrovertible statutory violations, the agency apparently accepted the insurer's assurance that the MPN was "not an issue." If documented violations of state law don't trigger enforcement, questionable MPN-based denials at scale certainly won't.

In practice, a payer can systematically deny bills by baselessly citing MPN non-membership, be wrong a substantial portion of the time, and face nothing worse than the mild inconvenience of denying Second Review appeals.

Consequences for Employers

Payers face no repercussions for MPN abuse. Instead, the ultimate consequences fall on California employers.

When providers reasonably conclude that treating patients covered by a particular insurer means fighting for reimbursement for authorized, in-network services, with no recourse if the appeal is denied, they stop accepting those referrals.

Providers can opt out of workers' comp; employers cannot. They can choose their insurer, but they cannot compel that insurer to honor its obligations to the providers treating their injured employees. Either way, employers keep paying premiums, up 8.7% in 2025 and proposed to rise another 10.4% in 2026, to fund a system that increasingly fails to deliver care.

Next week, daisyNews examines the CA DWC’s public MPN registry, which providers should be able to use to confirm MPN membership and fight improper denials. The degree to which this registry is non-functional surprised even us.

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