Australia's highest profile unionist, Paul Howes, will resign from the union movement on Monday.
Sources within the Australian Workers Union confirmed on Sunday night that Mr Howes, its national secretary, would announce his departure.
It was not clear if Mr Howes, who could not be reached for comment on Sunday night, would stand down immediately or see out the remainder of his term as head of the union.
The AWU national executive is meeting in Perth this morning. Mr Howes is expected to hold a press conference early afternoon east coast time after meeting his executive.
He was re-elected its national secretary only last year. Mr Howes, 32, is engaged to Qantas executive Olivia Wirth and has, since announcing their relationship, been unwilling to comment on issues relating to the airline – in which his union has hundreds of members. Mr Howes and Ms Wirth will marry in April.
In September last year, Mr Howes pulled out of a bid to take a Senate seat to be vacated after the 2013 election by former foreign minister Bob Carr after hostile reaction from some Labor MPs.
Mr Howes' failure to secure pre-selection for the vacant Senate seat, which led to him falling out with his factional ally, former NSW Labor secretary and now Seantor Sam Dastyari, is said to be a key reason for his disaffection with the labour movement.
Mr Dastyari, current NSW Labor Party secretary and Shop, Distributive and Allied (SDA) workers union national secretary Joe de Bruyn threw their support behind former lower house MP Deb O'Neill, who re-emerged to take the Senate seat.
Mr Howes' relationship with Mr Shorten, now the Labor opposition leader, was damaged after Mr Shorten switched support to Mr Rudd before the 2013 federal poll.
The union leader also enraged many in the union movement in February when he called for a ''grand compact'' between unions and business in a speech that also created a political headache for Mr Shorten.
Mr de Bruyn paid tribute to Mr Howes work with the union but said the decision to go could dent his future political ambitions.
''I regard him as a person of enormous potential and I told him that while he obviously commented on political affairs, if he stayed in the trade union movement he would go a long way,'' he said.
''It makes it much harder for him to get into the political arena because he will no longer have a union base to launch his career in politics.
''There has been speculation around for a while [that he could quit] but it does come as a big surprise to me.''
Federal Education Minister Christopher Pyne on Monday singled out Mr Howes for his policy ideas, saying he would be welcome in the nation’s parliament.
''He certainly has a lot more ideas about the future of Australia and what needs to be done about policy than the current crop of people who represent the Labor Party in Canberra,'' Mr Pyne told reporters. ''He would be very welcome here, but that is a matter for the Labor Party.''
Mr Howes has led the union since 2007 when Mr Shorten entered Parliament and is expected to be replaced by assistant national secretary Scott McDine. He leaves the union movement as the Abbott government launches a royal commission into union corruption.
Often touted as a ''faceless man'', his support for former prime minister Julia Gillard was instrumental in her toppling of Kevin Rudd in June 2010. He stayed loyal to Australia's first female PM in her leadership battles with Mr Rudd.
In November 2010, Mr Howes wrote Confessions of a Faceless Man: Inside Campaign 2010, an autobiographical analysis of the election and 18 months in Australian politics.
Apart from his AWU role, Mr Howes is deputy chairman of Australia's largest industry super fund, AustralianSuper, a member of the Labor Party's national executive, vice-president of the ACTU, director of the Chifley Research Centre and the McKell Institute and represents the Asia Pacific Region on the executive committee of the IndustriALL Global Union.
The Australian Financial Review reports that Mr Howes is expected to resign from all of his political duties.