New Zealand Prime Minister Jacinda Ardern has fired Workplace Relations and Safety Minister Iain Lees-Galloway after revelations of an “inappropriate relationship” with a former staffer.

Less than two months before the September 19 election, Ms Ardern fired her Labour colleague, who was also immigration minister, for “not modelling the behaviour I expect as a minister”.

Ms Ardern summoned the 41-year-old to her office on Tuesday after being forwarded a series of allegations from the opposition leader’s office.

Without disclosing many details in an attempt to protect the privacy of the staff member, Ms Ardern said she lost confidence in Mr Lees-Galloway given the nature of the pair’s working relationship and his ministerial responsibilities.

“I am weary about making moral judgements here. For me this is about conduct within a particular set of ministerial expectations,” she said.

“In undertaking this relationship he has opened himself up to an allegation of improperly using his office,” Ms Ardern said.

“Parliament is a place where we maintain standards.

He has not modelled the behaviour I expect as a minister.”

Ms Ardern said politicians should pay for their mistakes, not their families. Photo: Getty

Ms Ardern ended her official statement with a final comment requesting consideration for the family of Mr Lees-Galloway.

Politics is a place where we do need to maintain standards, and politicians should pay the price for mistakes, their families should not,” Ms Ardern said. 

“I do ask that we try and maintain that distinction.”

Mr Lees-Galloway, who is married with three children, told the Labour leader the year-long affair was consensual but accepted the PM’s call in a brief written statement.

“I have acted completely inappropriately in my position and cannot continue as a minister,” he said.

Mr Lees-Galloway has also decided not to stand at the next election.

-with AAP