If the U.S. Supreme Court decides to allow a question about citizenship to appear on the 2020 Census form, will it discourage people from answering it?

Many think it will — including the Census Bureau itself, immigrant advocates, and states and cities across the country, including Philadelphia, New Jersey, and Pennsylvania. Now, the federal government is testing that hypothesis.

Late last week, the Census Bureau began mailing census questionnaires to about 480,000 households asking for their citizenship status and other information that it plans to gather nationwide in the 2020 Census. The bureau will measure responses in this subset of the population to help it refine its strategy next year for following up with residents who do not answer their questionnaires. This test census — mandatory for those who receive the forms — will continue through August.

Dozens of cities, states, and counties have sued the Trump administration in an attempt to block a question about citizenship from the 2020 Census. Communities with large numbers of immigrants especially oppose the question because they worry their residents will not respond out of fear or protest and will not be counted in the census. Each decennial census decides the distribution of hundreds of billions of federal dollars, the boundaries of voting districts, and each state’s share of seats in the U.S. House.

The Supreme Court is expected in the coming weeks to decide whether to allow the question — last asked in a decennial census 70 years ago.

As with the 2020 Census, in addition to online, households can answer questions by mail and phone, using a code on their invitation to participate in the test. Residents who answer the test questionnaire this year still must answer next year’s census questionnaire, which also is mandatory.

In the years leading up to a decennial census, the Census Bureau tests aspects of the process to better prepare for the 10-year count. For 2020, the bureau started conducting yearly tests in 2015. A test in West Virginia, for example, was meant to measure how internet connectivity rates affected census participation rates. The 2020 Census will be the first in which the bureau encourages residents to respond online.

The Census Bureau is keeping some aspects of the test under wraps.

“As a federal statistical agency, it is important to maintain a neutral testing environment so we are limiting certain details about the 2019 Census Test," the bureau said in an emailed statement.