The most common and most likely answer to this crossword clue is the 9 plus 4 letter word ELECTORAL ROLL
I've seen this crossword clue in The Times
E
L
E
C
T
O
R
A
L
R
O
L
L
More clues leading to the result ELECTORAL ROLL
Buddy explains!
The straight part
We know that "Something upon which you can vote" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something upon which you can vote = electoral roll.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.