BIRMINGHAM, Ala. — Hispanic voters and civil-rights groups have asked to join a lawsuit to defend the practice of including in U.S. Census counts people who are in the country illegally.

Alabama and U.S. Rep. Mo Brooks sued the Census Bureau and the U.S. Commerce Department in May, arguing the predicted 2020 census numbers will cause the state to lose a congressional seat and an electoral vote to a state with a “larger illegal alien population.”

It has been a long-standing practice to include all U.S. residents, including noncitizens regardless of immigration status, in the census, which also determines the number of congressional seats for each state. In 2016, the U.S. Supreme Court ruled against two Texas residents who argued their votes were diluted by the practice of using the “whole population” to draw legislative district lines.

Alabama is seeking to have the practice declared unconstitutional. The state argues it violates existing statutes that “require a census enumeration of the total of legally present resident population.”

The Mexican American Legal Defense and Educational Fund filed a motion on Thursday on behalf of six voters and the group Chicanos Por La Causa, which are seeking to join the case as defendants.

They say they live in states, including California, Florida, Texas and Arizona, that could lose congressional seats and federal funding if the count doesn’t include all residents.

They fear the federal government will not fight for their interests in the case because it has “no specific incentive to defend the use of a particular population base” when it comes to configuring congressional seats. Instead, the motion says, the government’s stake is limited to defending the criteria and procedures used by the Census Bureau.