BOSTON — Backed by abortion rights groups, three Massachusetts women sued Wal-Mart Stores Inc. on Wednesday, accusing the retail giant of violating a state regulation by failing to stock emergency contraception pills in its pharmacies.

The lawsuit, filed in state court, seeks to force the company to carry the morning-after pill in its 44 Wal-Marts and four Sam Club stores in Massachusetts.

The plaintiffs argued that state policy requires pharmacies to provide all "commonly prescribed medicines."

Wal-Mart carries the morning-after pill in Illinois only, where it is required under state law, said Dan Fogleman, a spokesman for Bentonville, Ark.-based Wal-Mart.

Fogleman said the company "chooses not to carry many products for business reasons." He would not elaborate. But in a letter to a lawyer for the plaintiffs, a Wal-Mart attorney said the store chain does not regard the drug as "commonly prescribed."

CVS Corp., the state's largest pharmacy chain, stocks the pill at all of its drugstores.