According to Dictionary.com
When preceded by the, percentage takes a singular verb: The percentage of unskilled workers is small. When preceded by a, it takes either a singular or plural verb, depending on the number of the noun in the prepositional phrase that follows: A small percentage of the workers are unskilled. A large percentage of the crop has spoiled.
Your sentence contains neither the
, but to my ear it sounds closer to the indefinite article rule rather than the definite article rule, which would mean that it takes the plural verb.