the prohibition contemplated in the constitution , however , has reference to such requirements , as the virginia poll tax , invalidated in harper vs. virginia board of elections , 9 or the new york requirement that to be eligible to vote in a school district , one must be a parent of a child enrolled in a local public school , nullified in kramer vs. union free school district , 395 u.s. 621 , which impose burdens on the right of suffrage without achieving permissible estate objectives .