The question hasn't been included on a census since 1950.
The addition of that question has been blocked three different times in federal courts. In a ruling earlier this month, one judge said adding the question is "underscored by the lack of any genuine need for the citizenship question."
Some officials are worried the question would lead to disproportionate responses to the census, which is unconstitutional. The U.S. Constitution says an accurate tally of the population has be done every 10 years. But, if people are worried they may be kicked out of the country if they say they're not a U.S. citizen, they're less likely to respond to the census.
But the Commerce Department argues that the Constitution doesn't have a "standard by which a court can judge the propriety of such questions based on their impact on response rates or the accuracy of enumeration."
The Census Bureau says it needs to know if it can include the citizenship question on the 2020 census by June at the latest.