Labour leader Ed Miliband will tell the TUC he is "absolutely determined" to change union membership in the party to an opt-in system.
Addressing TUC members on Tuesday, Mr Miliband will tell the conference:
We need to build a party truly rooted in the lives of all the working people of Britain once more.
That is what my reforms are about. It is the right thing to do. We have to change.
And I am absolutely determined to make this change happen.
Mr Miliband's reform of trade unions would no longer see members automatically affiliated with Labour, as happens now.
Unions, though, fear the changes will relegate them to "placard carriers and cheque writers" and weaken or even sever the historic link with the party.
More top news
Approaching Atlantic frontal systems will give a wet and windy night right across the UK.
Star Trek's Captain Kirk said he will not be able to say a final goodbye to Mr Spock because of a charity commitment in Florida.
China's wild Panda population grew by 268 or 16.8% between 2003 and 2013 according to a nationwide survey on the highly endangered mammal.