The Labour Party is heading for a dramatic showdown over its leadership within days.
An angry David Shearer intends to confront the threat to his leadership by telling David Cunliffe this week to put up or shut up regarding a challenge to his job.
Sources said Mr Shearer's patience with the front-bench MP has been exhausted after Mr Cunliffe all but confirmed he would seek to exploit a rule change in Labour's constitution approved by the party's annual conference this weekend.
The new rule means Mr Cunliffe now only has to get the backing of 13 other MPs in the 34-strong Labour caucus to trigger a leadership vote in February which would take place under the party's new electoral college system.
That system is sought to favour Mr Cunliffe.
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Under existing rules, the party's caucus is required to re-endorse Mr Shearer's leadership in February anyway.
Rather than allowing things to drag on until then, Mr Shearer intends forcing the issue, probably by bringing the caucus vote forward.
He is mulling over various options, but is likely to bring matters to a head within days.
The Shearer camp is fearful that unless the discord over the leadership is settled once and for all, the undermining of the leader and the continued ructions that is causing within the party will start to seriously damage Labour's chances of winning the 2014 election.