America's two biggest pharmacy chains said Friday they will begin dispensing prescription abortion pills in a limited number of states where it's legal.

The move greatly broadens availability of mifepristone, even as a legal case over whether the drug was properly approved two decades ago now rests before the Supreme Court.

A CVS spokesperson told AFP: "We'll begin filling prescriptions for the medication in Massachusetts and Rhode Island in the weeks ahead and will expand to additional states, where allowed by law, on a rolling basis."

Walgreens "expects to begin dispensing within a week" in New York, Pennsylvania, Massachusetts, California, and Illinois, the company said on its website.

"But in the interests of pharmacist and patient safety, we will not disclose the number of sites per state nor identify the pharmacies that are dispensing," it added.

The Food and Drug Administration (FDA) authorized pharmacies to carry mifepristone in January 2023, with Friday's announcements the result of a long certification process.

Mifepristone was initially restricted to use at in-person locations, but was broadened to include mail-delivery during the Covid pandemic.

It works to block a pregnancy and is authorized for use through ten weeks of gestation, while a second drug, misoprostol, provokes bleeding to empty the uterus and was already widely available in pharmacies.

- Election battleground -

The news was hailed by President Joe Biden, who has made protecting reproductive rights a key part of his re-election campaign against the likely Republican candidate Donald Trump.

Trump tipped the balance of the Supreme Court during his own presidency and paved the way for reversal of the national right to abortion.

"With major retail pharmacy chains newly certified to dispense medication abortion, many women will soon have the option to pick up their prescription at a local, certified pharmacy -- just as they would for any other medication," Biden said in a statement.

"The stakes could not be higher for women across America. In the face of relentless attacks on reproductive freedom by Republican elected officials, Vice President Harris and I will continue to fight to ensure that women can get the health care they need."

Susan B. Anthony Pro-Life, a major anti-abortion group, slammed the move, while the Expanding Medication Abortion Access (EMAA) Project called for other major retailers to quickly follow suit.

- Improves access for women -

The US Supreme Court overturned the nationwide right to abortion in 2022, allowing each state to pass its own laws governing the procedure.

Twenty-one states have since banned or moved to restrict abortions to limits tighter than before Roe v Wade, the case law that previously upheld the constitutional right to terminate a pregnancy.

Abortion pills remain illegal in states where the procedure is prohibited. But women who decide to travel to a state where abortion is legal may now find a pharmacy much closer than an abortion clinic.

The Supreme Court will hear arguments on March 26 in a case brought by anti-abortion groups to restrict access to mifepristone, first approved in the year 2000 and used by more than 5.6 million Americans since.

Abortions administered as pills sent in the mail are just as safe and effective as those provided in person, a study published in Nature Medicine found in February.

It looked at data from more than 6,000 abortions using pills supplied by online clinics in 20 states between April 2021 and January 2022, finding there were no "serious adverse events" in 99.8 percent of these medical abortions and no follow-up care was needed in 98 percent of cases.

Polls repeatedly show a clear majority of Americans support continued access to safe abortion, even as conservative groups push to limit the procedure -- or ban it outright.