National Party MP Simon O'Connor has been backed by Labour and Green Party colleagues after his suitability to head an inquiry into euthanasia was questioned because of his personal beliefs.
Mr O'Connor is the chairman of Parliament's health committee, which is considering a petition to legalise euthanasia in New Zealand.
The devout Catholic, who once trained for the priesthood, is firmly opposed to assisted suicide.
Act Party leader David Seymour, who supports a law change, said Mr O'Connor had been too partisan on the issue and should step down as chairman.
Mr Seymour blamed Mr O'Connor for the committee's terms of reference, which he said had placed too much emphasis on suicide.