(CNN) — Demonstrators are expected to gather in cities across the United States on Saturday to protest the White House’s “zero tolerance” immigration policy that has prompted the separations and detentions of migrant families.

Here’s what you need to know about the Families Belong Together rallies.

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What is it?
The Families Belong Together event is billed by organizers as a nationwide day of action to protest the Trump administration’s strict immigration policies and call for the reunification of families separated and detained as a result of those policies’ implementation.

Hundreds of marches are expected to cap several weeks of outrage over the policies that have resulted in more than 2,500 immigrant children being separated from their parents in the weeks since the federal government started prosecuting anyone who crosses the border illegally.

Who is organizing the event?
MoveOn, the American Civil Liberties Union, the Leadership Conference on Civil Rights and the National Domestic Workers Alliance are the lead partners sponsoring the event, according to the FAQ on MoveOn’s website.

They’re joined by dozens of other organizations lending a hand, too, per the Families Belong Together website. Amnesty International USA, the Anti-Defamation League, the Southern Poverty Law Center and the Women’s March are among them.

What do demonstrators want?
According to a document outlining the Families Belong Together messaging strategy, protesters have three primary demands:

  • They want separated migrant families to be reunited immediately
  • They want the government to end family detentions
  • And they want the Trump administration to end its “zero tolerance” immigration policy

Despite the fact that President Trump signed an executive order last week reversing his administration’s family-separation policy, more than 2,000 children were still waiting to be reunited with their parents as of June 26, causing further anger and accusations that the administration is taking too long to take action.

“Since the beginning, President Trump has shown callous disregard toward mothers, fathers, and children who only want to find safety,” Amnesty International USA’s tactical campaigns manager Ashley Houghton said in a press release.

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“Last week’s executive order presents a false choice to people seeking protection. Detaining families is not the solution to ending family separation. Every family approaching the border must be treated with dignity and respect,” Houghton said. “The administration must end the cruel and unnecessary practices of family separation and detention.”

Where are the marches taking place?
The main march is taking place in Lafayette Square in Washington, D.C., across the street from White House. Thousands of people have indicated they will attend or expressed interest in attending the event on Facebook.

Hundreds of other rallies are being held by local organizers in all 50 states. Protesters will show up in US cities such as Los Angeles, New York, Chicago and Dallas, as well as in San Juan, Puerto Rico. There are also a handful of marches slated to take place in international cities such as Munich, Germany.

What will happen at the events?
The groups are asking march attendees to wear white as a “striking visual symbol” to bring participants together and “channel historic social justice movements unified by one color of clothing,” the FAQ says.

Demonstrators are also asked to bring their friends and a sign with a messages expressing support for the reunification of separated families, bearing messages like, “Keep Families Together” or “Familias Unidas No Divididas.”

MoveOn has additional information and resources available on its website.

After June 30, organizers say they’ll continue working until their demands are met. The end goal is to change the way immigrant families are treated in the years to come.

“We will keep working to re-imagine a new future where our families and loved ones are together to live freely and with dignity,” the groups say, “not separated or put in camps or cages.”

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