Republican attorneys general in 20 states warned CVS and Walgreens this week against mailing abortion pills in their jurisdictions, indicating that they would take legal action.

“We emphasize that it is our responsibility as State Attorneys General to uphold the law and protect the health, safety, and well-being of women and unborn children in our states,” the attorneys general said in letters to the nation’s two largest drugstore chains Wednesday.

“Part of that responsibility includes ensuring that companies like yours are fully informed of the law so that harm does not come to our citizens,” the attorneys general warned.

The Food and Drug Administration approved mifepristone more than 20 years ago as a safe and effective way to terminate an early pregnancy. The FDA says scientific and real-world evidence demonstrate that the pill is safer than surgical abortion and childbirth.

The drugstores said last month that they are applying to become certified with the FDA to dispense the prescription pill in states where it is legal to do so.

CVS and Walgreens’ decision comes after the FDA recently changed its rules to allow retail pharmacies to dispense the pill for the first time as long as the prescription comes from a certified health-care provider.

CNBC has reached out to the companies for comment on the letters.

The pill, mifepristone, has become a central focus in the battle over abortion in the wake of the Supreme Court’s decision last June to overturn Roe v. Wade, which protected access to the procedure as constitutional right for 50 years.

A dozen states have basically banned abortion since the Supreme Court’s ruling. Other states have restrictions on mifepristone that conflict with FDA regulations on the medication.

The Biden administration last month issued a legal opinion arguing that the Postal Service can mail the pill to states where it is banned if the sender does not intend to break the law.

The Justice Department argued that even in states with severe restrictions on abortion, there are exceptions where mifepristone would be legal. The DOJ opinion came in response to a request from USPS, asking how it should navigate an 1873 law called the Comstock Act which prohibits sending anything used to terminate a pregnancy through the mail.

But the attorneys general dismissed the Justice Department opinion as “bizarre” and said they expect the courts to uphold their view that mifepristone cannot be sent by mail in their states.

There are several pending legal cases over the FDA’s approval of mifepristone. GenBioPro, one of the pill’s manufacturers, has sued to overturn West Virginia’s abortion ban, arguing that FDA approval of drugs pre-empts state law.

Anti-abortion physicians have sued the FDA in a federal court in Texas to completely pull mifepristone from the U.S. market. The FDA has called that lawsuit “extraordinary and unprecedented” and warned that a decision in the physicians favor would harm its approval powers.

The letters to CVS and Walgreens were signed by the attorneys general of Missouri, Alabama, Alaska, Arkansas, Florida, Georgia, Indiana, Iowa, Kentucky, Louisiana, Mississippi, Montana, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Texas, Utah and West Virginia.