WASHINGTON, DC – Can the U.S. census ask each person in the country if he is an American citizen? The Supreme Court will hear arguments on that question on Tuesday.

The Enumeration Clause in Article I of the Constitution requires a nationwide census be taken every ten years. The Census Act empowers the head of the Commerce Department to determine what the census will ask, aside from the number of persons residing at every address in the nation. Commerce Secretary Wilbur Ross decided for the Trump administration that the census will ask each person in the nation next year if that person is a citizen of the United States.

That was a recurring question on census forms until recently. The first census to ask about citizenship was the one conducted in 1820, and the last was 1950. After 1950, the Census Bureau – which is part of the Commerce Department – has continued to ask that question on the “long form” census form that goes to some census-takers, as well as on its yearly questionnaire that goes to a small number of households each year, called the American Community Survey (ACS).

However, when Ross put that question on the 2020 census, leftwing partisans sued, claiming that inserting this question violates the Administrative Procedure Act (APA). More surprising to many, Judge Jesse Furman of the U.S. District Court for the Southern District of New York agreed, writing a 277-page decision (which is shockingly long) holding that it is illegal to ask about citizenship.

The Trump Justice Department appealed to the U.S. Court of Appeals for the Second Circuit. But knowing that the census forms must be finalized by July 2019 to be ready for nationwide use in 2020, Solicitor General Noel Francisco petitioned the U.S. Supreme Court to grant “certiorari before judgment,” which would bypass the New York-based Second Circuit.

For the first time in many years, the Supreme Court granted the petition to take the case immediately. The justices ordered an expedited briefing schedule and set the case to be argued April 23.

There are three issues in the case. The first is whether it violates the APA for the census to ask about citizenship. The second is whether courts can look beyond the administrative record to probe the thinking of top-ranking government officials in an APA case. The justices inserted a third issue of their own, asking whether asking that if the APA allows the question, would that question nonetheless violate the Enumeration Clause.

In other words, the case is about whether asking about citizenship violates either federal law or the Constitution, and also whether it is out of bounds to chase down a member of the president’s Cabinet in such lawsuits.

This case has very significant implications. Legislative districting lines for Congress and statehouses are based on census data. Dozens of congressional seats and perhaps hundreds of state seats could shift if states drew lines based on citizenship, instead of total numbers of persons. Some even argue that congressional seats, and with them Electoral College votes for president, could be reallocated among the states based on citizenship data. At minimum, billions of dollars in federal spending is based on census numbers.

Not only that, but there is a federal database that tracks the whereabouts of every legal alien in this country. If the government were to know the address of every alien in the nation, and could subtract out every legal alien, then the U.S. government could know the whereabouts of almost every illegal alien in the nation. There are currently legal barriers to sharing census data within the government, but if those obstacles could be successfully navigated, it could have an extraordinary impact on immigration enforcement.

The Court will decide the case by the end of June.

The case is Department of Commerce v. New York, No. 18-966 in the Supreme Court of the United States.

Ken Klukowski is senior legal analyst for Breitbart News. Follow him on Twitter @kenklukowski.