The Biden administration has told hospitals that they "must" provide abortion services if the life of the mother is at risk.
Officials say federal law on emergency treatment guidelines pre-empts state laws in jurisdictions that now ban the procedure without any exceptions following the Supreme Court's decision to end a constitutional right to abortion.
The Department of Health and Human Services cited requirements on medical facilities in the Emergency Medical Treatment and Labour Act (EMTALA).
The law requires medical facilities to determine whether a person seeking treatment may be in labour or whether they face an emergency health situation - or one that could develop into an emergency - and to provide treatment.
"If a physician believes that a pregnant patient presenting at an emergency department is experiencing an emergency medical condition as defined by EMTALA, and that abortion is the stabilising treatment necessary to resolve that condition, the physician must provide that treatment," the agency's guidance states.
"When a state law prohibits abortion and does not include an exception for the life of the pregnant person - or draws the exception more narrowly than EMTALA's emergency medical condition definition - that state law is pre-empted."
The department said emergency conditions include "ectopic pregnancy, complications of pregnancy loss, or emergent hypertensive disorders, such as preeclampsia with severe features".
"It is critical that providers know that a physician or other qualified medical personnel's professional and legal duty to provide stabilising medical treatment to a patient who presents to the emergency department and is found to have an emergency medical condition pre-empts any directly conflicting state law or mandate that might otherwise prohibit such treatment," HHS Secretary Xavier Becerra wrote in a letter to healthcare providers.
The department says its guidance does not reflect new policy, but merely reminds doctors and providers of their existing obligations under federal law.
"Under federal law, providers in emergency situations are required to provide stabilizing care to someone with an emergency medical condition, including abortion care if necessary, regardless of the state where they live," said Centres for Medicare & Medicaid Services Administrator Chiquita Brooks-LaSure.
"CMS will do everything within our authority to ensure that patients get the care they need."