Gerard Coyne, who stood against Len McCluskey to be leader of Unite, has been sacked by the union.
Mr Coyne, Unite's West Midlands Regional Secretary, was suspended just before the result of the election was announced in April.
He lost the election, but is challenging the result with the Certification Officer.
Mr Coyne said he was notified by email that he has been sacked from his position following a disciplinary hearing.
A Unite spokesman said: