Nearly a dozen senators are calling on the Department of Veterans Affairs to take action that improves Health Net's interactions with providers in the Veterans Choice program.

Health Net Federal Services, a Centene subsidiary, offers Medicaid managed care plans to more than 2.9 million military families and partners with the VA to coordinate the Veterans Choice and Patient-Centered Community care programs.

In the letter (PDF) to Secretary David Shulkin, 11 senators led by Jon Tester, D-Mont., and Mike Crapo, R-Idaho, said they're "fed up" with the way Health Net oversees veterans' programs, adding that the VA is "ultimately responsible for the Health Net's poor performance."

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Providers in the senators' states who deal with Health Net face long waits for reimbursement—if they get reimbursed at all, according to the letter. Many of those providers are small, according to the senators, and carry high VA balances as they await responses from Health Net.

"Our home state providers deserve better than the miserable customer service provided to them by Health Net, which appears to be devoting even less attention to the Choice Program as its expiration nears," the senators wrote.

"Moving forward, we expect VA to take immediate action to address our concerns so that the provider experience is improved," they added.

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The senators called on the VA to push Health Net to respond promptly to providers—some faced hourslong waits, according to the letter—and follow up with requests for assistance on paperwork promptly.

Health Net was recently targeted by the Office of Personnel Management's Office of Inspector General for refusing to comply with a planned audit of its IT systems. The office's OIG said the refusal was "unprecedented," and failure to complete the audit leaves questions about its IT vulnerabilities unanswered.

The Veterans Choice program was instituted following the 2014 nationwide scandal that revealed many veterans faced extremely long waits for care at VA facilities. In the program, veterans can seek care at non-VA providers when they face long wait times or travel distances.

But it has been financially troubled of late, and the VA has planned an overhaul of the program to expand options for veterans.