The woman claimed the officer later started calling her and visiting her house, where he touched and rubbed himself on her.
The NZPCA summary said the matter was historic as the woman had been too scared to speak out until now.
The woman’s complaint was lodged with the Independent Police Conduct Authority (IPCA), the government agency responsible for monitoring police activities.
IPCA case resolution manager Sarah Goodall confirmed preliminary investigations had been launched.
“We have received a complaint and are in the process of assessing the matter and making further enquiries before determining how the authority will proceed,” she said.
Inspector Donna Laban, senior professional standards manager at police national headquarters, said police had been notified of the complaint and a formal process was underway.