Police are investigating three reports of indecent assault at a Wellington gym's Christmas party last year.
The women said they were sexually assaulted and one of them was drugged during the night by one of the trainers.
Police said they were taking the allegations seriously but were still gathering evidence and speaking to witnesses.
"Officers are actively following a number of enquiries to establish the circumstances of the incident."
The gym has written to its staff and members informing them of the complaint and subsequent investigation.
It said the complaint was about one of the trainers after its Christmas party in December.
"We took this complaint seriously and started an investigation immediately."
The gym said it looked at phone records, footage of the night from the gym and bar in question and accounts of both the complainants and witnesses.
"While the investigation upheld some parts of the complaint, we did not feel we had enough evidence to make a finding in relation to other parts of the complaint."
It said the investigation had not been closed, and the "preliminary outcome" had been communicated to the complainants along with what action they intended to take against the trainer.
The gym told staff that the police investigation was almost complete and they would wait for that outcome before proceeding.
It said it was committed to finding a way forward.
Police have asked people to refrain from talking about the incident on social media.
"Police understand that these allegations are concerning, but we ask that people do not use social media to name individuals or post personal details, as this could impact on the police investigation."
No arrests have been made at this stage.
Where to get help
If you have been affected by sexual violence and need support contact Wellington HELP on their 24/7 support line, 04 801 6655.
Victim Support 0800 842 846
Rape Crisis 0800 88 33 00
Mosaic - Tiaki Tangata Peer support for males who have experienced trauma and sexual abuse: 0800 94 22 94