29 CFR §2590.715-2719(A)(b)(1-2)

(1) If a group health plan, or a health insurance issuer offering group health insurance coverage, provides any benefits with respect to services in an emergency department of a hospital, the plan or issuer must cover emergency services (as defined in paragraph (b)(4)(ii) of this section) consistent with the rules of this paragraph (b).

(2) General rules. A plan or issuer subject to the requirements of this paragraph (b) must provide coverage for emergency services in the following manner –

(i) Without the need for any prior authorization determination, even if the emergency services are provided on an out-of-network basis;

(ii) Without regard to whether the health care provider furnishing the emergency services is a participating network provider with respect to the services;