Labour leader Andrew Little would not outline possible sanctions or comment on whether Mr Shearer could be stripped of his foreign affairs portfolio.
"There is a range of options. I don't want to go into any of them, but it is important he understands, and that every caucus member understands, that caucus collective responsibility is real and it's got to stand for something.''
It follows comments Mr Shearer made to the Herald in support of the TPP, just days after Labour's caucus had decided it would oppose any legislation required for the TPP.
The sanctions could depend on Mr Shearer's willingness to back down from his stance and are likely to range from a reprimand and apology to being stripped of his portfolio and demoted. As foreign affairs spokesman, Mr Shearer sits on the foreign affairs select committee which will be considering the TPP.
Although fellow MP Phil Goff also spoke in support of the TPP, Mr Little said he had agreed Mr Goff could break ranks with the party because of his long-standing support for the trade agreement as Trade Minister when the talks kicked off.
Mr Little expected to deal with Mr Shearer, who is a former Labour leader, soon. ``I've had one discussion with David so far just to ascertain the facts. I'm yet to have a further discussion with him about what happens now, but I think every caucus member knows caucus collective responsibility is utterly vital and there has to be some sort of consequence if that is breached.'' Mr Shearer said he did not want to comment.
Mr Little believed Mr Shearer had the potential to be one of the best foreign affairs ministers New Zealand had ever had.
"I certainly have that ambition for him and I'd like to see him in that role.''
The treatment of Mr Shearer differs from that of Mr Goff, whose comments rubbished claims the TPP was an unacceptable infringement of New Zealand's sovereignty - the very reason Labour is opposing it.
However, Mr Little has confirmed Mr Goff had a dispensation which allowed him to break the party line. Asked if he had told Mr Goff to at least stop speaking publicly on the issue, Mr Little said he had discussed it with Mr Goff and "I'm confident we have a shared understanding about that''.
He said most people recognised Mr Goff was the trade minister who initiated the negotiations and had a "deep-seated``view on it.
Mr Goff is running for the Auckland mayoralty so no longer has a ranking within Labour's caucus.
