WilmerHale and the American Civil Liberties Union (ACLU) of Massachusetts successfully convinced the US government to release Lucimar de Souza, a non-citizen who had been detained by Immigration and Custom Enforcement (ICE) for more than three months, separating her from her US citizen husband and 10-year-old son. De Souza and her family are among many other families represented by WilmerHale in a proposed class action challenging the government's efforts to separate married couples and families pursuing lawful immigration status.

In January, de Souza and her husband attended their interview with the US Citizenship and Immigration Services to confirm their marriage for her lawful immigration status. Although the marriage petition was approved, de Souza was detained by ICE officials immediately after the interview, and since had been held at the Suffolk County House of Corrections in Boston. At a hearing held by Judge Mark Wolf of the US District Court for the District of Massachusetts in early May, WilmerHale and ACLU of Massachusetts argued that de Souza's detention was unconstitutional and in violation of the ICE's own regulations. During a break, when it became clear that the judge was going to rule against it, the government agreed to release de Souza on May 8, just in time for Mother's Day. Even after the government announced its intent to release de Souza, the judge ruled that ICE had violated its own regulations and de Souza's procedural due process rights.

De Souza is represented by a WilmerHale team including Partner Kevin Prussia, Counsel Michaela Sewall, Senior Associates Jonathan Cox and Stephen Provazza and Associate Colleen McCullough. Cox argued for de Souza's release during the hearing.