Ed Miliband has described union members as the "backbone of Britain" but insisted Labour's relationship with the unions "must change" as he delivered his keynote speech to the TUC conference in Bournemouth.
Mr Miliband's speech generated ripples of polite clapping instead of rapturous acceptance as ITV News' Political Editor Tom Bradby reports:
Mr Miliband said he was "absolutely determined" to drive through the controversial reforms - which would require union members to opt in to Labour affiliation as individuals rather than being automatically signed up by their unions - but admitted introducing the changes represented a "massive challenge".
Unions have warned Miliband that the reforms could cost Labour millions of pounds a year in affiliation fees, while the GMB has already announced it will cut its payments by around £1.1 million from January.
However the Labour Leader stated his belief that the changes could boost party membership from 200,000 to 500,000 or more:
Unison leader Dave Prentis said "lectures" about the challenge facing the historic link were a "turn off."
Mr Miliband made a number of pledges which pleased unions, including legislating on zero hours contracts, not building any new free schools, and keeping the East Coast rail line in public ownership.
Len McCluskey, leader of Unite, said his promises were "beginning to seal the deal" with workers, adding: "We look forward to getting more meat on the bone."
TUC General Secretary Frances O'Grady said praised the speech saying: "Ed Miliband's warm reception reflected his understanding of the concerns of the modern workplace - the squeeze in living standards and the growth of exploitation through zero-hours contracts."