The Trump administration last week announced that it would add a citizenship question to the decennial census in 2020, citing the need for more granular data for determining Voting Rights Act violations. Critics say that adding the question could cause some immigrants — particularly those who are not citizens — not to respond, resulting in an undercount.

There is no reliable data to estimate how many people would opt out of the census, but a panel of experts from inside the United States Census Bureau still expressed opposition to the move, in part because of concerns about accuracy.

“Just because there is not clear evidence that adding the question would harm the census accuracy, this is not evidence that it will not,” they wrote in a memo.

Noncitizen share of population Wash. 2% 6 8 12 14 Me. Mont. N.D. Minn. Vt. Ore. N.H. Idaho Wis. S.D. N.Y. Mass. Mich. Wyo. R.I. Conn. Iowa Pa. Neb. N.J. Nev. Ohio Md. Del. Ill. Ind. Utah W.Va. Colo. Calif. Va. Kan. Mo. Ky. N.C. Tenn. Okla. Ariz. N.M. Ark. S.C. Ala. Ga. Miss. La. Tex. Fla. Alaska Hawaii Noncitizen share of population 2% 6 8 12 14 WA ME MT ND VT MN OR NH ID NY WI MA SD MI RI WY CT PA IA NE NJ NV MD OH IL IN DE UT WV CO VA CA KS MO KY DC NC TN OK AZ NM AR SC AL GA MS LA TX AK FL HI Source: Jeffrey Passel, Pew Research Center estimates based on 2014 American Community Survey

About 56 percent of the nation’s 44 million immigrants are not United States citizens, and an estimated 45 percent of noncitizens are undocumented. Among those who are not citizens, undocumented immigrants have the lowest rates of participation in census surveys in general, experts say.

Accurate census counts are critical for many functions, including the disbursement of billions in federal and state dollars and the distribution of congressional seats and representation in state and local governments. A group of 17 state attorneys general and seven cities filed a lawsuit Tuesday to block the change.

An undercount of population could affect federal funding to states.

A recent Census Bureau report found that 132 programs used decennial census or related data to distribute more than $675 billion to states in 2015. Most of the money was related to health care, education and assistance for the poor.

Top federal assistance programs distributed using census data Medicaid and other medical assistance $312 billion Supplemental Nutrition Assistance Program (SNAP) $71 Medicare Part B physician payments $70 Highway planning and construction $38 Pell grant program for students $30 Federal school lunch program $19 Temporary Assistance for Needy Families (TANF) $17 Section 8 housing vouchers $16 Title 1 grants to local school districts $14 Grants to states for services for students with special needs $11 Head Start early childhood program $9 Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) $6 Source: Census Bureau via Rockefeller Institute of Government

A significant level of nonparticipation could affect congressional seats.

Some academics have created hypothetical scenarios to show how a reduction in participation could affect the distribution of congressional seats among states, which are determined by total residents, not just citizens.

States That Could Lose Seats Total seat change by percentage of Hispanic noncitizens who do not respond PROJECTED SEATS IN 2020 10% 100% Florida 29 –1 California 53 –1 –2 –3 Texas 39 –1 –2 Arizona 10 –1 States That Could Gain Seats Total seat change by percentage of Hispanic noncitizens who do not respond PROJECTED SEATS IN 2020 10% 100% Montana 1 +1 Minnesota +1 7 Alabama 6 +1 Ohio 15 +1 West Virginia 2 +1 Virginia 11 +1 Michigan 13 +1 States That Could Lose Seats Projected seats in 2020 Total seat change by percentage of Hispanic noncitizens who do not respond 10 100 Fla. 29 –1 Calif. 53 –1 –2 –3 Texas 39 –1 –2 Ariz. 10 –1 States That Could Gain Seats Projected seats in 2020 Total seat change by percentage of Hispanic noncitizens who do not respond 10 100 Mont. 1 +1 Minn. 7 +1 Ala. 6 +1 Ohio 15 +1 W.Va. 2 +1 Va. 11 +1 Mich. 13 +1 Source: Maxwell Palmer, Boston University

According to Maxwell Palmer, an assistant professor of political science at Boston University, if 10 percent of Hispanic noncitizens opted out, Florida could lose one congressional seat, and Montana could gain one. In an extreme case, in which 100 percent of Hispanic noncitizens did not participate, a total of seven congressional seats could be reshuffled, with three lost by California and two by Texas, Dr. Palmer said.

Andrew A. Beveridge, a Queens College sociologist, warned against overstating the potential effects of the citizenship question. He said that the maximum share of noncitizens who do not respond would be 20 percent, which is not enough to trigger a huge change.