Judicial Watch has gotten involved in a lawsuit brought by Louisiana to prevent the inclusion of illegal aliens in the census count for purposes of apportioning seats in the House of Representatives. I doubt the courts are the way to go; previous lawsuits have been thrown out for lack of standing, though how a state that will lose (or fail to gain) a House seat due to the inclusion of illegals in the count doesn’t have standing is beyond me.
In any case, if we’re going to exclude illegals from the 2020 census count used for apportionment (not from the census altogether), Congress needs to start acting now. By the time the census approaches, all important decisions will already have been made. It seems to me that the plain language of the 14th Amendment bases apportionment on the “whole number of persons in each state,” so further amendment would be required. My own preference would be to exclude non-citizens in general, not just illegal aliens, from the count for apportionment. It’s easier to do (you just ask “Are you a citizen of the United States?” — and if we purge the obnoxious race/ethnicity questions, there’ll be plenty of room on the form) and it’s more defensible, since it’s the Congress of the United States we’re talking about, and if you’re not a citizen of the United States, whatever your particular status might be, it’s not your Congress.