Four leading organizers of “A Day Without a Woman,” a day-long strike for women’s rights, were arrested Wednesday during an act of civil disobedience in New York City.

Linda Sarsour, Tamika Mallory, Carmen Perez, and Bob Bland (who were also the lead organizers of the Women’s March on Washington) were arrested after blocking traffic outside Trump International Hotel in Columbus Circle.

The organizers were released Wednesday night. Bland, who recently gave birth, was the last to be released. After Sarsour was released, she told the Huffington Post she was upset Bland was still being held, because Bland was “expressing her milk in the sink” and needed to nurse her baby.

Nonetheless, Sarsour said, “I feel empowered, I feel proud of what I did today. ... I hope it sends a message to people that you’ve got to risk it, you’ve got to be bold in this moment.”

A total of 13 organizers and supporters of A Day Without a Woman were arrested Wednesday, according to a spokesperson.

The Women’s March account live-tweeted the arrest, including a selfie inside the police van:

We are blocking traffic as a form of civil disobedience in Columbus Circle (outside Trump Hotel). #DayWithoutAWoman — Women's March (@womensmarch) March 8, 2017

We are not sure what precinct we are being taken to at the moment. But we are together, reSisters. #DayWithoutAWoman pic.twitter.com/r10WBikdl8 — Women's March (@womensmarch) March 8, 2017

The arrests happened after a large rally supporting A Day Without a Woman in downtown Manhattan.

Demonstrators have been protesting both in public and in private, by taking the day off work, wearing red, refusing to shop, or attending rallies.

The purpose of the “strike” is to make the world appreciate women’s work — which is systematically undervalued — by taking away that work for a day. It’s also a demand for women’s equality and policies like paid family leave, a $15 minimum wage, and full abortion rights.

These organizers are trying to use the Women’s March as a starting point for a bigger movement

A Day Without a Woman was the fourth of 10 major protest actions that the recently arrested Women’s March organizers are leading during President Trump’s first 100 days in office.

“We want to reintroduce the notion of strike in the political lexicon of this country,” Lamis Deek, a human-rights attorney and one of the organizers of the Day Without Women, told Bloomberg.

Organizers hope to keep up the huge grassroots momentum that drew more than 4 million people worldwide to protest for women’s rights the day after Trump’s inauguration, and they hope to turn that momentum into longer-lasting political power.

They have a huge list of supporters who said they wanted to stay involved in activism after the march was over. In just over a month, the Women’s March has also managed to turn itself into an organization with a big email list and big potential staying power.

Sure, organizers have put a lot of effort and promotion into A Day Without a Woman — but the Women’s March should still have plenty of other tricks up its sleeve once March 8 has come and gone.

Technology has helped the Women’s March build a ton of capacity in a short time. And it’s not just Facebook and other social media; those tools are great at spreading the word about events, but not so great for long-term community organizing.

The Women’s March website and email list is managed through Action Network — a platform only available to progressive activists, and one that is specifically designed to help organizers channel scattered grassroots energy into something more focused.

“The Women’s March is a great real-world example of what we were trying to build from the beginning,” Brian Young, executive director of Action Network, told Vox. The march got started with completely disconnected grassroots Facebook events, he said — but the organizing really took off once the march had a central organizing hub where activists could register their own local events or find ones nearby.

The second of the “10 Actions for the First 100 Days” events was about helping activists organize local strategy meetings, or “huddles.” Young thinks these huddles were just as impressive and important as the original march, even though they involved fewer people overall and got almost no media attention.

“They had about 5,000 huddles. There are organizations that have been around for decades that can’t get people to come to 5,000 events,” Young said. “They had this base of support and knew hundreds of people who were willing to step up and organize their communities.”

A women’s general strike is still a huge, ambitious lift, one that could easily collapse under the weight of its own expectations. But at least in the modern era, it probably has better chances of succeeding now than ever before.