FILE - This March 23, 2018, file photo shows an envelope containing a 2018 census letter mailed to a U.S. resident as part of the nation's only test run of the 2020 Census.
FILE - This March 23, 2018, file photo shows an envelope containing a 2018 census letter mailed to a U.S. resident as part of the nation's only test run of the 2020 Census.

A second federal judge has ruled that the Trump administration's decision to add a citizenship question to the 2020 U.S. census is illegal.

Judge Richard Seeborg in San Francisco said Wednesday that the government's move was arbitrary and capricious and would violate a constitutional requirement that the census count everyone in the country.

Seeborg said evidence showed the question would result in a significant undercount of non-citizens and Latinos.

The effect of his decision is limited. A federal judge in New York had previously blocked the administration from adding the question to the population count, and the U.S. Supreme Court last month agreed to review that decision.

An email to the U.S. Department of Justice was not immediately returned.