Scott Morrison has refused to offer former Australia Post chief executive Christine Holgate an apology after she accused him of bullying.
The prime minister said he regretted the distress his "strong language" caused, but he did not believe there was a reason to call Ms Holgate and apologise.
Mr Morrison claimed her treatment had "nothing to do with gender" and there was nothing to suggest the Australia Post chairman should resign.
Ms Holgate left her position in October after it was revealed she gifted luxury watches to four senior executives as a reward for securing a major contract.
At the time, the prime minister told parliament he was appalled by the purchases and if Ms Holgate did not resign she could go.
"Parliament can get very willing and on that occasion my language was very strong and I do regret any distress that would have caused to Ms Holgate," he told reporters in Perth on Wednesday.
Ms Holgate said it was one of the worst acts of bullying she had ever witnessed.
"You would have rather hoped that before somebody publicly hung you and humiliated you, that they may pick up the phone and call you and ask you directly what happened and why," she said.
One Nation leader Pauline Hanson, a fierce supporter of Ms Holgate, savaged the prime minister's refusal to apologise.
"Given the prime minister won't apologise to Christine Holgate, it looks like the taxpayer-funded empathy training he's been paying for was a complete waste of time," Senator Hanson said.
Greens senator Sarah Hanson-Young, who is chairing an inquiry into Australia Post, said the prime minister should phone Ms Holgate and apologise.
Senator Hanson-Young also called on Australia Post chairman Lucio Di Bartolomeo to be sacked for his role in the saga.
"The treatment that Christine Holgate was given in comparison to the backing that the PM has given men who have behaved badly in his own government is just so stark," she told ABC radio.
Businesswoman Lucy Turnbull has described the way Ms Holgate was treated by the prime minister as disgraceful and an example of misogyny.
"She was treated disgracefully and I can't help thinking there was a bit of gender bias in the way she was treated," Ms Turnbull told the ABC.
"I'd like anyone else to argue the contrary and point to a man who's been treated like that."
The prime minister denied treating Ms Holgate differently because of her gender.
"I don't accept there are any gender-related issues here at all," Mr Morrison said.
He tried to blame Labor for forcing his hand after asking questions about the Australia Post board.
But Opposition Leader Anthony Albanese said Ms Holgate's fate was sealed as soon as the prime minister opened his mouth.
"He effectively sacked Christine Holgate on the floor of the parliament. After that answer, of course, how could she continue?" Mr Albanese told reporters.
"Scott Morrison always looks to not accept responsibility for his own actions. He owns this."
There are suggestions Ms Holgate was targeted because she opposed a secret plan to privatise the lucrative parcel delivery service at Australia Post.
Unions have urged the prime minister to rule out breaking up key parts of the postal service, which Ms Holgate warned would cost thousands of jobs.
Australian Associated Press