Deputy Labour leader Harriet Harman will issue a plea for unity to union leaders at the annual TUC gathering.
Ms Harman will urge TUC members to unite behind Ed Miliband's plans to reform their historic links with the party, or risk a Tory general election victory.
Her speech comes amid ongoing hostility surrounding the proposed changes, and the continued fallout from the Falkirk selection-rigging scandal.
More top news
British Airways passengers face tighter restrictions on the size of hand luggage as part of changes to their inclusive baggage allowances.
The wrestling hall of fame star 'Rowdy' Roddy Piper has died aged 61.
Labour has called for compensation from the French government to be paid to Britons affected by the chaos at Calais.