This Tuesday, the U.S. Supreme Court will hear arguments on whether the Department of Commerce may include a citizenship question as part of next year’s U.S. Census. Experts say including this question would result in as many as 6.5 million people declining to fill out and return their Census forms, particularly among immigrant and people of color communities, with children disproportionately among those left out.

You may recall that important things emerge from the U.S. Census, which takes place every ten years. The numbers determine how many members of Congress each state has (and, therefore, how many Electoral Votes in a presidential election). They influence the apportionment of political districts ranging from congressional level and state legislative to city council, county district, and school board. They are even used in shaping the contours of the precinct in which you live.

And census data is used in appropriations – more than $800 billion annually for everything from community health centers to roads to affordable housing and day care.

Census data is used in ways you may not be aware. As the Washington Post recently noted, “The decennial census data is also the baseline against which virtually all other surveys are calibrated. Which means that whatever its motives, the administration’s innumeracy is likely to skew all sorts of other critical information that government agencies use to evaluate economic trends and health epidemics; that businesses rely on to decide how much to invest and hire and where; and that workers and families use to determine where to live, what to study, how much to spend on a home.”

Just how important is an accurate census? Just how important is Tuesday’s U.S. Supreme Court case?

Beth Lynk, the Census Counts Campaign Director for the Leadership Conference Education Fund, puts it this way: “This may be the issue you haven’t heard of that may determine the outcome of everything you care about.”

This is particularly true for human needs advocates. An adverse decision – resulting in a severe undercount – would mean program funding is less likely to reach low-income communities with the greatest need for health care, housing assistance, education, and other services. These low-income communities may face diminished political representation at the city and county level, in state legislatures, and in Congress, likely undermining future efforts to target services appropriately. All of this is why human needs advocates are going to be showing up at 10:30 a.m. Tuesday in front of the U.S. Supreme Court – to send a message that a fair count matters. It is why a diverse coalition of groups have come together to ensure a fair and accurate census. It is why nearly 150,000 Americans submitted comments to the Department of Commerce with regard to the citizenship question, with 99.1 percent opposing it.

And it is why so many have filed amicus briefs with the Supreme Court in opposition to the citizenship question, including Democrats and Republicans, states and localities, professional scientific organizations, former Department of Justice officials, businesses, faith-based groups, civil rights organizations, the philanthropic community, and more.

So how did this question get to the Supreme Court? And what exactly is going to be argued on Tuesday?

For several years now, Commerce Secretary Wilbur Ross has been angling to add a citizenship question to the U.S. Census. His argument is that the Department of Justice needs the statistics in order to better enforce the Voting Rights Act. The problems with this argument are numerous – one could write an entirely separate piece enumerating them – but here are two big ones: an undercount would make the Voting Rights Act harder to enforce, not easier, and U.S. District Judge Jesse Furman called Ross’ action a “pretextual or sham justification.”  Ross started out wanting the citizenship question, and pressed the Justice Department to ask for it to provide a cover rationale.

Lawsuits opposing Ross’ efforts sprang up almost immediately. Thus far, the Trump Administration is 0-3 in these lawsuits – three U.S. District Judges, from California, Maryland, and New York – have ruled against Ross. No judge has ruled in favor, and because the case was fast-tracked to the Supreme Court, no federal appellate court has fully weighed in.

Generally, there are two legal arguments at issue. The first is whether Ross and the Department of Commerce violated the Administrative Procedure Act, by acting in an “arbitrary and capricious” manner.  At a hearing last month before the House Committee on Oversight and Reform, fireworks erupted when Ross once again offered his explanation that the citizenship question would provide information helpful in enforcing the Voting Rights Act.

“Mr. Secretary, you lied to Congress, you misled the American people, and you are complicit in the Trump Administration’s intent to suppress the growing political power of the nonwhite population,” Rep. William Lacy Clay (D-MO) told him.

The second legal argument goes more directly to the U.S. Constitution. It asserts that the citizenship question violates the enumeration clause and 14^th Amendment of the Constitution, which states, in part, “Representatives….shall be apportioned among the several States…according to their respective Numbers…,” elsewhere requiring a count of “the whole number of persons in each state,” whether or not they are citizens. In other words, Census counts and the resulting apportionment are expected to be based on real numbers, not a politically manipulated severe undercount.

So what happens next? The Supreme Court will be under pressure to rule quickly; Census forms must be printed in June. In the meantime, please visit CHN’s Census page to learn more, and watch a recording of the webinar held in January by CHN and the Leadership Conference on Civil and Human Rights. In addition, here is a digital toolkit prepared to help individuals and groups prepare for, and respond to, Tuesday’s arguments.