ACC inadvertently sent a woman another person's claim review on the very same day the Privacy Commissioner announced an inquiry into ACC privacy breaches.
Stacey Parenti, a Canterbury student, said she sent her claim to the resolution service for review after ACC refused it.
She received her claim back by post, but also in the envelope was another woman's claim.
She did not read the other woman's information but rang ACC and was told to send the information back or destroy it.
"I am so concerned about my information being leaked to other people," Parenti said. "They really need to tighten up their procedures. This other woman would have no idea that her information is being sent out to random people."
This latest breach happened on March 23, the day the Office of the Privacy Commissioner and ACC jointly commissioned an inquiry after claimant Bronwyn Pullar received 6000 claims by email.
ACC's Stephanie Melville refused to comment during the inquiry.