The New Zealand First MP Ron Mark has been hospitalised and is undergoing medical tests after suffering a suspected mild heart attack.
Mr Mark has been at the centre of a political storm over his sexual relationship with a 15-year-old girl when he was a 17-year-old soldier.
His family says he is in a comfortable condition and expects to undergo further tests during the next few days.
Ron Mark, a list MP and the NZ First chief whip, has had to endure the controversial release of information about his private life in recent weeks.
It had earlier been claimed, by NZ First leader Winston Peters, that the country's top soldier, Major General Maurice Dodson, had accessed Mark's army file.
He served in the Army for 20 years, and, as an officer, commanded the Sultan's Special Force Electrical and Mechanical Engineers from 1986 to 1990.
The NZ First leader believes the information in the file was going to be used to coerce Mark. He says if he had not made the file public, someone else would.
Mark was convicted of unlawful sexual connection with the girl, who was his girlfriend and whom he thought was of legal age.
Ron Mark has been openly critical of Major General Dodson - accusing him of playing too much golf on a trip to Asia and questioning government spending on new army vehicles.
Mark and Dodson both appeared before a State Services Commission inquiry last week investigating defence leaks.
The inquiry is expected to conclude in about two weeks.