Shares of managed care companies with exposure to the Affordable Care Act's health insurance exchanges sold off during morning trading on Oct. 13 after news broke that subsidy payments meant to help reduce ACA premiums would no longer be disbursed to insurers.

In a late-night statement on Oct. 12, Centers for Medicare and Medicaid Services Administrator Seema Verma said the White House was overstepping its legal bounds by paying the subsidies, known as cost-sharing reduction payments, because Congress never appropriated money for them.

Centene Corp.'s stock declined by about 10% minutes after the market opened, though it did make up some of that ground shortly thereafter. Shares of the company, which has pivoted its strategy to focus more on the ACA exchanges than other health insurers, were down about 5.85% to $88.20 as of 11:00 a.m ET.

Shares of Molina Healthcare Inc. were also lower at 11 a.m., sliding about 4.15% to $60.78. Anthem Inc.'s stock was down about 2.64% to $184.73. The company has withdrawn from state ACA marketplaces where it was losing money, but still offers plans in many counties, including some where it is the only insurer selling ACA plans.

Athenahealth Inc., a technology company that works with hospitals and service providers, was down 4.46% to $115.58 as of 11:00 a.m. ET.

Shares of other major managed care companies that are less involved in the ACA marketplaces or have stopped selling the plans altogether, including UnitedHealth Group Inc., Aetna Inc. and Humana Inc., were down less than 2% during mid-morning trading.