On Wednesday, the coalition government pledged $24 million over four years to the charity's initiative, Gumboot Friday.
National committed to the funding boost as part of its coalition agreement with New Zealand First.
Public records show the chairperson of I Am Hope, Naomi Ballantyne, donated thousands to the National Party in recent years.
In 2020, she donated $20,600 to National's campaign. Ahead of last year's election, she made three separate payments totalling $6,840.
Ballantyne only became chair of the charity earlier this year, months after the coalition agreement had been signed.
RNZ has contacted Naomi Ballantyne for comment but has not received a response.
In a statement to Stuff, Ballantyne said she had no influence over the funding decision or the commitment in the coalition agreement.
"[The] previous chair Sir Ian Taylor had resigned and I suspect Mike chose me because he knew he needed a greater level of business and governance experience to meet the expectations that would be required for any recipient of government funding," Ballantyne said.
"I have not spoken with anyone from any party about this funding until yesterday's meeting with Minister [Matt] Doocey relating to the announcement.
"I have been working with the director general responsible for mental health, Robyn Shearer, to determine the reporting requirements that we will be required to meet in the contract, as you would expect of me in this role."
Labour's Ingrid Leary described the situation as "disturbing".
"It's tin-pot politics and it appears that all roads lead to the National Party."
The mental health sector needed "strategic investment, not opportunistic, friendship-informed decision making", Leary said.
"We can't know what's happened here because he hasn't been a fair and transparent process. So it would be better for everybody if that process had been followed before announcements were made. It's unfair to the sector.
"This is not about Gumboot Friday. This is about fairness and transparency, and the diminishing of trust in our democratic processes."
Prime Minister Christopher Luxon said any suggestion the situation could be considered a conflict of interest was "outrageous and ridiculous".
"That's not what's happening here, it's got nothing to do with it and it's outrageous and ridiculous, frankly, if the Labour Party want to make that accusation.
"Mental health is not something that you politicise ... mental health and an organisation like Gumboot Friday, who do a great job, get a great benefit and a great return. That's a very good investment for this government to be making in a community organisation like that."
