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
NASA has given the green light to an emergency space walk to repair a broken-down computer attached to the International Space Station.
A necklace blessed by Buddhists helped a British woman become the youngest female to scale Mount Everest from both sides, she claims.
Celebrities including Leonardo DiCaprio have holidayed there - and even former US President Barack Obama is a fan.