A bitter battle over funding reforms could boost Conservative Party support and help keep David Cameron in Downing Street, Labour's deputy leader Harriet Harman will warn trade union leaders.
Speaking tonight at TUC Congress in Bournemouth Ms Harman will say how "disappointed" she was by the GMB's decision to reduce Labour party funding by over £1 million.
We all need to think carefully about who gains from any falling out and any division.
And we need to remember that fundamentally we're fighting for the same things - that we are on the same side.
If we don't have unity, there are going to be winners and losers. The winners will be the Tories and the losers will be our constituents and your members. This is a dangerous moment.
The change that Ed is proposing is not to weaken the relationship between Labour and the trade unions - it is to make it a reality.
We must work together to shape and deliver that change.