"I've heard what some of my colleagues saw that day. We are pretty resilient here in Christchurch but never in a million years did any of us expect to be dealing with a mass shooting," the nurse said.
She was one of hundreds of nurses slamming the union on social media for their lack of support, with some saying they were "disgusted and disappointed".
"On the day of the tragedy we had an email from NZNO saying it was a difficult time and they would have a support service available from Monday at 8am.
"My first thought when I saw that email was 'seriously? ... it's Friday and you are saying you can help us but not until Monday, that's ludicrous',"the Christchurch nurse said.
She said the DHB had offered support services but it would have been nice if the union had shown face on the day of the tragedy, knowing their members had not dealt with this level of trauma before.
Instead, members received a combined email from the DHB and NZNO thanking them for their efforts, and providing further phone numbers for trauma support.
Moments later, another email landed, letting members know their subscription fees were increasing by 1.8 per cent by April 1, 2019.
Musa said members were first told about the increase in November, then in December and again in January.
"We had an obligation to notify our members of the increase and failing to do so would have been a breach.
"Yes, in hindsight we could have held the email but the email was written on Friday when we didn't know the extent of the incident," Musa said.
Within two days, many members had jumped ship, resigning from the NZNO and signing up with Nurses Society of New Zealand (NSNZ) - including high-profile advocacy group Nurse Florence.
The group wrote on Facebook: "Following the recent events and the final insult from NZNO in not being there for their frontline workers at a time of a national tragedy, myself and my #hear our voices moderators have decided to resign from NZNO and have joined the Nurses Society of New Zealand (NSNZ)."
Another nurse shared their resignation letter for others to follow, saying: "Having identified the tragedy, the scale of the crisis and the direct toll to the nurses you represent, yet delaying your own action to duty, I can no longer in good faith support your organisation."