Legal advocates at Georgetown University Law Center filed a constitutional challenge Tuesday on behalf of millions of children who are U.S. citizens and have been denied $500 coronavirus economic relief payments because one or both of their parents are undocumented immigrants.

The lawsuit argues that a provision of the federal Cares Act “violates the equal protection principles” of the Fifth Amendment by prohibiting payments for children of parents who file taxes using an individual taxpayer identification number (ITIN), a substitute for a Social Security number that is used mostly by immigrants without legal status.

The lawsuit named Treasury Secretary Steven Mnuchin as a defendant and asked a federal judge in Maryland to impose an immediate injunction and grant class-action status to plaintiffs, who seek payment under the $2 trillion stimulus package passed in March.

Demographers estimate that 80 percent of the 5 million children of immigrants in the United States illegally are born in this country to parents who are employed in industries undergoing mass layoffs. Their parents, according to advocates, are also likely to be in high-risk jobs that keep society running — such as meatpacking, farming, food production, and restaurant and custodial work, as well as personal services including health and child care.

“Immigrants make up almost a fifth of front-line workers during this pandemic. It is an absolute outrage that we are relying on immigrant families to care for our loved ones and provide our essential supplies and yet denying their children the support they are entitled to as U.S. citizens,” said Nicholas Katz, senior manager of legal services for Casa, a D.C.-area immigrant advocacy organization that helped bring the lawsuit filed by the law center’s Institute for Constitutional Advocacy and Protection (ICAP).

A spokeswoman for the Justice Department did not immediately respond to a request for comment.

Other federal lawsuits have been filed seeking a nationwide injunction blocking the restrictions on stimulus payments to U.S. citizens married to illegal immigrants, saying the prohibition violates the constitutional rights to free association, due process and equal protection.

Under the law, payments are granted to families only when all filers on a tax return and their qualifying children have Social Security numbers. Even if U.S. citizen children and one parent have a Social Security number and the other parent does not, the parents must file separately to receive a payment, an option that often imposes a higher tax burden, the lawsuit said.

“The refusal to distribute this benefit to U.S. citizen children undermines the Cares Act’s goals of providing assistance to Americans in need, frustrates the Act’s efforts to jump-start the economy, and punishes citizen children for their parents’ status — punishment that is particularly nonsensical given that undocumented immigrants, collectively, pay billions of dollars each year in taxes,” ICAP legal director Mary McCord, a former U.S. Justice Department official, said in a statement.

According to the lawsuit, the Cares Act provision is resulting in “the intentional and discriminatory exclusion of U.S. citizen children” from cash assistance as the country faces a historic unemployment crisis.

The lawsuit was brought on behalf of four Maryland families with seven children under age 9, who were identified only by their initials under federal court rules for minors.

Their parents include two working mothers who filed taxes on gross earnings last year of less than $25,000 and $35,000, respectively; a third mother who is a full-time caretaker for her children; and a married couple with a 7-month-old. The couple filed taxes last year on earnings of less than $150,000.

But for the provision, the families in the lawsuit would have received $1,200 per adult and $500 for each dependent child in their household under 16 — a “financial lifeline” that could be used for food and rent. In one case, a family could be eligible for up to $3,200 in aid.

The lawsuit says the mother of one 8-year-old plaintiff, identified as R.A.V.R., came from Mexico to the United States 15 years ago and lost her restaurant job in the District.

Her boyfriend, with whom she and her child live, contracted the coronavirus and has been under quarantine, as have her brother-in-law and his wife, who also live with her.

“I have lost my job, and in my home three adults have the coronavirus; none of us are working,” said Norma, whose last name was withheld by her attorneys for safety reasons. “My son is an American citizen, and we need him to receive the Cares Act benefit to provide food and a roof over his head until this difficult moment passes.”

The mother of another plaintiff, C.V., age 9, is relying on part-time work at a restaurant after the catering company she worked for closed, the lawsuit said. She is relying on community support and school-provided food while she cannot pay rent, the lawsuit stated.

The mother of four child plaintiffs, ages 3 to 8, received support from a family member who has now lost his job because of the pandemic, the lawsuit said. It added that she is relying on community support and a federal nutritional program for women, infants and children — popularly known as WIC — for her youngest child. She is also relying on her neighbor’s Internet plan so her older children can keep up in school.

For the married couple listed in the lawsuit, the father is commuting four hours a day to keep his job with an employer in a “financially precarious position” and despite “serious health concerns,” the complaint alleged.

Several other federal safety net programs reach U.S. citizen children of undocumented immigrants, including earned income tax benefits, welfare, food stamps, the WIC program and housing aid, the lawsuit noted.

Villanova University law professor Leslie Book, an expert on poverty and income tax law who joined ICAP attorneys in filing the lawsuit, called the Cares Act exclusion “a slap in the face to millions of hard-working taxpaying immigrants who comply with our tax laws, file tax returns and pay billions of dollars in taxes. . . . This is especially cruel and unjust when so many are struggling to pay for food, rent and medicine.”