Mr Shearer said he wanted to move on from the leadership debate that arose last weekend and he had the full support of his caucus.
Mr Cunliffe was demoted to the back bench and stripped of his portfolios after attempting to undermine Mr Shearer's leadership.
Mr Shearer told TVNZ's Q + A programme today that the leadership question "came to a head" at the conference.
"Unfortunately what happened was we had a very, very successful conference that was overshadowed by David Cunliffe talking about leadership and not being able to loyal to me as the leader, that's why I took the action I did.
"As far as I'm concerned, I'm ruling a line under it and we're moving on from here."
He said he was "dismayed" to see Mr Cunliffe acting disloyally.
"I don't feel I can trust him and as a result of that I have demoted him to the backbenches and we are moving on from there."
Mr Shearer said at Tuesday's caucus meeting 100 per cent of the MPs endorsed his leadership.
"That's about as good as it gets."
Labour MPs have been gagged from speaking about Mr Cunliffe's punishment, with Mr Shearer appointing himself as the sole spokesperson on the issue.
But there has been anger from some of Mr Cunliffe supporters on Facebook and the Standard blog as well as calls for MPs who had publicly criticised Mr Cunliffe to also be punished.
One of Mr Cunliffe's New Lynn electorate committee members, Greg Presland, said the committee had concerns about the demotion and the criticisms by other MPs, such as the chief whip Chris Hipkins.
