Luxon told Morning Report that National never supported the legislation.
"We believe it's voters, not party leaders, that should actually decide who New Zealand MPs are.
"I just think that gives the party leader way too much power in that regard."
If elected, National would repeal the law, although it would have other priorities.
As far as the Uffindell inquiry was concerned, Maria Dew QC has begun work and will take two weeks to compile her report.
Luxon said his decision on the MP's future and the rationale behind it would be made public, but in fairness to both sides involved in the allegations, individuals' submissions would remain private.
No further allegations about Uffindell had arisen, he said.
Luxon did not want "to pass any judgements" on the Sharma situation, saying it was a matter for the Labour Party and leader Jacinda Ardern.
In defence of the removal of the top tax rate of 39 per cent on income over $180,000, which National announced several weeks ago, Luxon said there were major shortages of critical people such as surgeons and engineers and it would help encourage them to move here.
However, it was not the only reason. He said even though a recent 1News-Kantar poll suggested half of National's supporters did not favour removing the top tax rate, National was the party of low taxes, and intended on repealing all seven taxes that Labour had introduced.
Luxon said the party was unapologetic about its belief that taxes should be lower.
"We want to unwind all those tax increases, and that will benefit everybody across the country."
