The U.S. Constitution requires a census every 10-years and the federal government will attempt its next nationwide headcount in 2020.

But before the census takers hit the streets, lawyers for the Census Bureau are headed for the U.S. Supreme Court at issue is a single question about citizenship on the census form.

The lower court ruled the question is unlawful because it may lead to an undercount of immigrants who fear they will be harassed or deported.

The Supreme Court will hear arguments about a single question on the 2020 census.

Hans Von Spakovsky with the Conservative Heritage Foundation says the Trump administration added the question because the government needs accurate data.

The census determines how congressional districts are drawn and how much federal money communities receive.

“That is very much dependent on knowing the citizenship population versus the non-citizenship population of the U.S.,” Von Spakovsky said.

“By asking the citizenship question they are going to deter people from coming forward,” Richard Cohen said.

Richard Cohen with the Southern Poverty Law Center says the citizenship question may lead to an undercount of immigrants who fear they will be harassed or deported.

The Supreme Court will hear the case in April.

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