(CNN) The Southern Poverty Law Center has joined a class action lawsuit against the government on behalf of more than 10,000 undocumented children held in detention centers across the country.

The lawsuit, filed by the SPLC, Legal Aid Justice Center and Washington, DC-based Sterne, Kessler, Goldstein & Fox PLLC, seeks that detained children who have a sponsor in the US be released from detention and that the system is overhauled.

At issue is the sharing of a sponsor's information with Immigration and Customs Enforcement and a leaked government memo that revealed the motivation of policies, like "zero tolerance" and information sharing, was to deter migrants.

"The memo did play an important role in having us understand the motivation of the administration," said Mary Bauer, deputy legal director at the SPLC in a call with reporters on Tuesday. "It seemed to us apparent that the policies were designed for the purpose of harming families and those concerns were confirmed."

In the same call, Kayla Vazquez, a detained child's sponsor who's listed in the complaint, described the challenges she and her family have faced in trying to retrieve her husband's cousin, a 17-year-old boy from Honduras who was apprehended at the US-Mexico border last summer.

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