Unite has announced it has suspended Angela Rayner from her membership of the union, amid a deepening row over the long-running bin strikes in Birmingham.
The union said it would also re-examine its relationship with Labour after an emergency motion at its conference in Brighton.
The deputy prime minister has been urging striking bin workers to accept a deal to end the dispute tabled by the Labour-run city council.
Mountains of rubbish have been seen across the city since bin collection workers walked out in January, with an all-out strike going on since March.
Unite is a major donor to the Labour Party, and has previously donated to Rayner herself.