The resignation of Labour President Nigel Haworth was "inevitable" and he has acted as a "fall guy" for the Prime Minister, Simon Bridges says.
The National Party leader said Prime Minister and Labour leader Jacinda Ardern has "done the least possible every step of the way - it's just wrong".
"He's been caught," he said, referring to Haworth. "The Prime Minister needed a fall guy here, and he's it.
- Labour assault, bullying claims: Everything you need to know
- Jacinda Ardern 'deeply disappointed' in Labour's handling of allegations
- Exclusive: Labour forced to review investigation into bullying, sexual assault allegations against staffer
"But that won't make it go away because there are so many serious questions around who knew what and when in the Beehive, and also what happens in relation to this alleged perpetrator."
Bridges' comments came less than an hour after Haworth announced his resignation amid the Labour Party's handling of sexual assault allegations.
Ardern said she accepted his resignation after reading "incredibly distressing" reports of an alleged sexual assault involving members of the Labour Party.
"I discussed the correspondence with the Labour Party President this morning. Whilst he stands by the statements he has made on this matter, I believe mistakes were made."
The Prime Minister said this week she was told sexual assault allegations had not been raised with the Labour Party, despite emails showing a complainant had informed the party.
Bridges pointed out that the process took several months, and that the allegations had been in the media for several weeks. He said the Prime Minister should have made inquiries.
"It just beggars belief that she didn't know much more than she's led on in the last 24 hours or so," Bridges said.
"The person at the centre of all of this may not be in Parliament, but he is still working for the Prime Minister and that must be resolved."
A group of MeToo Labour members, some of them self-described as "survivors", say the resignation of Nigel Haworth is a good first step but doesn't go quite far enough.
"While this is a step towards acknowledging that Labour has failed these survivors, there is still much more work to do," MeToo Labour said in a statement.
"We are still calling on the Prime Minister to ensure that the other changes are implemented comprehensively. We are still calling on Nigel Haworth to apologise to the survivors for the handling of this process under his leadership."
Following the announcement of Haworth's resignation, the Prime Minister said the complainants still haven't gone to her, but she said she has made the offer to meet with them.
Ardern said the correspondence she read in the last 48 hours was "incredibly distressing" and confirmed that "allegations made were extremely serious" and that the process "caused complainants additional stress".
"These are deeply sensitive matters and it's clear to me from that correspondence that harm has been done and my job is to make that right," she said.
"Mistakes have been made. There's no denial of that, and that's why I'm offering an apology to the complainants...It should have been dealt with externally."
National's deputy leader Paula Bennett - who claims complainants have gone to her to be heard - asked the Prime Minister in Parliament if she stood by her comments made at the UN general assembler last year.
"Will she be revising her statement to the UN less than a year ago that MeToo must become WeToo, in light of her own office's failure to respond to sexual assault allegations involving one of her staff members?"
The Prime Minister replied, "No."