The giant Unite union is set to have its first female general secretary after a ballot to decide a successor to Len McCluskey.
Voting papers will be formally counted on Wednesday, but Sharon Graham, an assistant general secretary of the union, is expected to win.
It is believed she has achieved a few thousand more votes than Steve Turner, who had been tipped as the favourite candidate.
It is expected that the other candidate, Gerard Coyne, will come third.
A spokesman for Sharon Graham’s campaign said “The sampling of the vote is going on. The more it goes on the better it looks for us. Of course we will only get the result when the count is finished tomorrow.
“But we are confident Sharon is going to win it. If she does it will be an historic victory for the campaign and the workers in Britain and Ireland”.
Formal statements from the candidates are expected on Wednesday.