If the question does lead to an undercount, the effects could be profound. The census is used to allocate nearly $700 billion in federal money. As many as 16 states are positioned to either lose or gain a congressional seat, depending on the census results. California could lose even more than one seat if all the immigrants in the state illegally were to opt out of the census.
Source: Los Angeles Times March 27, 2018 14:57 UTC