Paul Howes' plan to enter Parliament was thwarted by a hostile campaign against him by members of the parliamentary Labor Party.
The high-profile union boss said on Thursday he wanted to avert a "destructive, divisive and messy fight" as he withdrew his bid to take Bob Carr's soon-to-be-vacant senate seat.
But Fairfax Media has learnt a bitter resistance to his move to Canberra had mobilised within the NSW Right, Mr Howes' own faction.
Members of the Right argued that the self-styled "faceless man" would be divisive and a road block to healing the rift between the Right factions of the NSW and Victorian branches, which bitterly split during the Kevin Rudd-Julia Gillard leadership wars of 2010 to 2013.
The NSW Right's wholesale switch to Mr Rudd this year was crucial to his retaking the prime ministership in June.
Some MPs feared Mr Howes would join Stephen Conroy and Wayne Swan as destabilising forces against the renewal that both Labor leadership candidates, Anthony Albanese and Bill Shorten, have been promising.
Fairfax understands there is also lingering resentment within parliamentary ranks at Mr Howes' outspoken opposition to Chris Bowen's introduction of enterprise migration agreements – temporary visas allowing mining companies to import foreign labour – which the union leader described as "lunacy".
He also fell out bitterly with Mr Shorten, his predecessor as national secretary of the Australian Workers' Union, over Mr Shorten's last-minute switch to Mr Rudd.
At a press conference attended by his fiancee, Qantas executive Olivia Wirth, Mr Howes acknowledged the force of the opposition he faced. "I recognise it would have been a destructive, divisive and pretty ugly and messy fight and, by jeez, I've had enough of the messy and ugly fights over the last three years."
Mr Howes' candidacy for the Senate was pushed hard by the NSW state secretary of the Australian Workers Union, Russ Collison. The Transport Workers Union and the National Union of Workers were also behind him and could probably have delivered the numbers for him.
But new ALP general secretary Jamie Clements stared down the push, telling Mr Howes that a female candidate was the best thing for the party, particularly as Labor's 40 per cent female quota is not being met.
That has left Deborah O'Neill, who lost her central coast seat of Robertson at the election, as the favourite to enter the Senate. With the loss of Dobell, Labor is keen to retain a presence on the central coast before a concerted effort to regain the area in 2016.
The alternative is Tara Moriarty, secretary of the liquor and hospitality union United Voice and vice-president of NSW Labor.
Senator Carr's former chief of staff, Graeme Wedderburn, has put himself forward. He said on Thursday he had Senator Carr's support.
Senator Carr, who is back in the country after a week's overseas break following the Group of 20 meeting of industrialised nations, would not comment. A spokesman said: "There is no vacancy and he said he will serve a full term."
Senator Carr is expected to announce his resignation some time before Parliament resumes in late October or early November.