A national civil rights advocacy group is suing the Trump administration on behalf of U.S. citizens denied government stimulus payments because they are married to undocumented immigrants.

The Mexican American Legal Defense and Educational Fund, or MALDEF, is alleging that a provision in the $2.2 trillion stimulus package known as the CARES Act that denies the benefit to mixed-status families in unconstitutional.

The benefits have been denied for married couples who jointly filed previous tax returns with one person using an Individual Taxpayer Identification Number. The number is often used by undocumented immigrants who don’t have legal authorization to work in the country.

The lawsuit argues that the CARES Act “discriminates against mixed-status couples because it treats them differently than other married couples, in violation of the U.S. Constitution’s Fifth Amendment guarantees of equal protection and due process” according a statement from MALDEF.

The lawsuit also alleges that by denying the benefit, the federal government is humiliating “Plaintiffs and the children of mixed-status couples by treating them adversely as compared to other families.”

There are six plaintiffs in the case, including Christina Segundo Hernandez, a Fort Worth resident who has four American citizen children and is married to an undocumented immigrant. Her case was first highlighted by The Dallas Morning News.

About 2.7 million Texans are U.S. citizens and have at least one undocumented family member, according to the Center for American Progress. The lawsuit names as plaintiffs U.S. Secretary of the Treasury Steve Mnuchin and U.S. Commissioner of Internal Revenue Charles Rettig.