Census finding it very hard to hire many Hispanics in Texas and other states?
But recruiting Latinos is hard for some of the same reasons they are difficult to count, recruiters say. Census workers must be proficient in English, pass a test to prove their math and map-reading skills, and preferably be U.S. citizens. (The bureau hires legal residents as a last resort if no citizens from a particular area are available.) In certain places, such as rural areas, Colonias or neighborhoods with a high proportion of undocumented immigrants "there may be a very small fraction who are eligible," said Mr. Salinas. . . .
The reason they can't find these workers then is because of the citizenship or legal resident citeria.
See also here for a discussion of how easy the test is and how they have dropped the drug test requirement.