With preparations for the 2030 census already underway, Trump said Thursday he has instructed his administration to start work on a “new” census.

According to a social media post by Trump, that census would exclude millions of people living in the country without legal status — an unprecedented change to how the country has conducted population tallies since the first U.S. census in 1790.

The 14th Amendment requires the “whole number of persons in each state” to be included in a key set of census numbers used to determine how presidents and members of Congress are elected.