The Trades Union Congress is set to appoint its first woman general-secretary to replace Brendan Barber, who retires later this year.
Frances O'Grady, currently No 2 in the organisation, is thought to be front-runner for the post, which will be decided at a meeting of the TUC's executive next month.
Although she could theoretically face a challenge, it is expected she will be elected unopposed. Both Mr Barber and his predecessor, John Monks, had served as the TUC's deputy. Paul Kenny, its president, said: "Brendan has made an immense contribution to the trade union movement."