Prime Minister John Key says MPs can cross the floor, or vote against their party, in Parliament if they want but National backbencher Tau Henare chose to toe the party line.
Henare said last night in Parliament that he was ''torn'' over voting against a Maori Party bill which would have allowed people to swear an oath to the Treaty of Waitangi.
He supported the words and emotion of the bill.
''Unfortunately the whipping system says that I cannot vote for his bill.''
Henare said he had considered crossing the floor - or voting against his party - but eventually did not.
He said the bill should have at least gone to select committee. ''I'd like to cross the floor.''
But that did not create stable government, he said. Voting down the bill meant we were the same as the ''other colonial nations''.
"This house of representatives had an opportunity to say to the world, yes there are different cultures, yes there are people in our nation and we could have said to the world that if you wanted to, not we're going to make you, but if you wanted to you could have sworn your allegiance on the Treaty of Waitangi.''
His great-grandfather, Tauerekareka Henare, had fought for similar ideals during his own time in Parliament, Henare said.
Key said he was not surprised by Henare's view.
''He had already said to me that he was opposed to the position that caucus took but respected the caucus view.''
Henare could have crossed the floor if he wanted to, Key said. ''I can't physically stop people.''
National believed the bill could have implications that would be difficult to uphold, he said.
Maori Party MP Te Ururoa Flavell said he was disheartened by the National Party's backtracking on its commitment to the Treaty.
''We had the courage, the good will, the commitment to promote the Treaty as our founding document for those who may have wanted to exercise that right - but when it came to the vote, National, New Zealand First, United Future and ACT walked away.''
National had closed down an opportunity for conversation.