Officials of Wal-Mart Stores Inc. (WMT) announced Friday the company will reverse its earlier policy and stock emergency contraception pills in all of its pharmacies effective March 20, saying the giant retailer could not justify being the country's only major pharmacy chain not to carry the morning-after pill.

The announcement comes after Massachusetts last month ordered the world's largest retailer to stock the so-called Plan B pill, following a lawsuit by three Boston women against Wal-Mart.

Illinois also requires pharmacies to carry the prescription drug, and those are the only two states where Wal-Mart has so far stocked emergency contraception.

"We expect more states to require us to sell emergency contraceptives in the months ahead," said Ron Chomiuk, vice president of pharmacy for Bentonville, Ark.-based Wal-Mart.

"Because of this, and the fact that this is an FDA-approved product, we feel it is difficult to justify being the country's only major pharmacy chain not selling it," Chomiuk said in a statement.

Chomiuk said the company will maintain its conscientious objection policy, which it said is consistent with the tenets of the American Pharmaceutical Association. The policy, except where prohibited by law, allows any Wal-Mart or Sam's Club pharmacy employee who does not feel comfortable dispensing a prescription to refer customers to another pharmacist or pharmacy.

Wal-Mart has more than 3,700 pharmacies in the United States, it said.

It has previously said it "chooses not to carry many products for business reasons," but has refused to elaborate. A Wal-Mart lawyer in the Massachusetts lawsuit said the company did not believe that emergency contraception was commonly prescribed or within the "usual needs of the community."

Plan B contains a higher dose of the hormones in regular birth control pills. It cuts the chances of pregnancy by up to 89 percent if used within 72 hours of unprotected sex. The earlier it's taken, the more effective it is.

If a woman already is pregnant, the pills have no effect. They prevent ovulation or fertilization of an egg; they also may prevent the egg from implanting into the uterus, the medical definition of pregnancy, although recent research suggests that's unlikely.

Some abortion opponents oppose emergency contraception because it blocks fertilization of an egg or because they believe it can block the fertilized egg from being implanted.

National women's and family planning groups called on Wal-Mart to change policy and start stocking emergency contraception pills in its pharmacies after the Boston lawsuit filed Feb. 1.

The groups, including the National Organization for Women, NARAL Pro-Choice America, Planned Parenthood and the National Council of Women's Organizations, said Wal-Mart did not have the right to overrule a doctor's prescription of emergency contraception for a woman.

Connecticut added pressure Thursday when Attorney General Richard Blumenthal said the insurance plan for 188,000 state employees and retirees should no longer cover prescriptions at Wal-Mart unless the retail giant agrees to stock emergency contraception pills.

Wal-Mart's critics welcomed the change.

"We commend Wal-Mart for taking an important first step towards allowing women access to safe and legal medication," Andrew Grossman, executive director of union-backed campaign group WalMartWatch.com, said in a statement.

WalMartWatch.com said Wal-Mart should now look at changing what it claimed were other business practices that harm women, including inequality in pay and promotions that are alleged in a class-action federal lawsuit against the retailer pending in San Francisco. Wal-Mart has denied those allegations.