Dozens of breast-feeding women plan to descend on the Hirshhorn Museum on Saturday for a "nurse-in" to highlight their federally protected right to nourish their babies in public.

The cause of the grass-roots gathering of lactivists: A Jan. 30 incident involving Noriko Aita, who was nursing her daughter on a bench in the Hirshhorn when she was informed by a Smithsonian security guard that she would have to move to the women's restroom.

Aita, a stay-at-home mother from Rockville, said she couldn't find anywhere to sit in the restroom, so she returned to the bench. The guard then told her to try sitting on the toilet. When she moved to another bench instead, another Smithsonian guard told her to stop.

"I was shocked," Aita said Tuesday as her 11-month-old, Elaine, chattered away. "What's wrong with nursing? But I wasn't sure of my rights and the law, so I told my husband: 'Let's just go home.' "

There, Aita jumped online and learned of the Right to Breastfeed Act, signed into law by President Bill Clinton in 1999 as part of an appropriations bill. The law ensures a woman's right to breast-feed her child on any federal property where she and her infant are otherwise permitted.

Benches in federally owned properties such as the Hirshhorn, for instance.

Cue the outrage.

"It's unacceptable," Aita said.

She told a friend from her Rockville moms group, who told other friends that they should march on Washington.

Word spread via mothers' Internet lists, lactation consultants, Facebook and the lively D.C. Urban Moms and Dads forum, where debates broke out: Is a nurse-in counterproductive? Is nursing in public acceptable in the first place? And, um, has anybody actually contacted the Hirshhorn?

The museum quickly apologized to Aita and posted a note on its Facebook page, saying it had made its "security staff aware of the federal law allowing women to breastfeed in any public or private location. . . . We regret that this incident occurred and we apologize for the frustration it has caused."

Still, the two-hour nurse-in will go on as planned, commencing at 10 a.m. Saturday, said organizer LJ Pelham, who has been thrilled with the Hirshhorn's response to Lactation-gate.

"We're not protesting against them; this is not to give them a black eye," she said. "The fact that they apologized is wonderful. But the nurse-in wasn't organized to elicit an apology. What happened to Nori happened because there was a lack of education and awareness. We want to ensure it doesn't happen to anybody else again."

Dozens of mothers and others have said they will attend the nurse-in.

Jennifer Myrna, who has never met Aita, plans to hand out hundreds of laminated cards with the text of federal and local breast-feeding laws. Aita will be there with her baby, perhaps sitting on the same bench where the kerfuffle began, she said. Pelham said she'll be "enjoying some of the art and nursing my daughter if she wants to. I'm expecting a calm, peaceful group."

Breast-feeding mothers regularly mobilize in support of their rights. A group of lactivists in Montreal came together last month to support a woman who had been asked to leave a children's clothing store while nursing her infant. In June, more than 100 mothers staged a nurse-in at the Francis Scott Key Mall in Frederick, after mall employees asked Ann-Marie Luciano to move to a designated nursing area. A national nurse-in was held at some airports in 2006 after a family was removed from a flight when the mother refused to cover her baby with a blanket while breast-feeding.

The fight goes on.

Elizabeth Lipinski, a Baltimore mother, was outraged when she heard what happened to Aita. She mentioned it to her husband, a painter and studio owner, then had a thought: Why doesn't the Hirshhorn celebrate the nurse-in by commissioning a piece?

"It would be great if they called an artist and asked them to do something," she said. "I love the idea of documenting the nurse-in with photographs and blowing them up huge and putting them on the walls of the museum. That's what museums do."