Prime Minister John Key says his MP Tau Henare never asked if he could cross the floor on a bill on legal oaths.
Maori Party MP Te Ururoa Flavell's legislation would have allowed people to refer to the Treaty of Waitangi when making legal oaths.
It was defeated by 69 votes to 52 with National, ACT, United Future and New Zealand First voting against it on Thursday.
However, National's Tau Henare made an impassioned speech in Parliament saying he supported the change, but could not vote for it as he was whipped by his party.
Mr Key was asked if he would have let Mr Henare vote against party position if the MP wanted to.
The Prime Minister said he did not know, but that he could not have stopped him and it would have been a decision for Mr Henare to make.
Mr Key said National was against the law change, as there could have been implications because of different interpretations of the Treaty of Waitangi.