The challenger in the election for the leadership of Unite has been suspended from his job in the trade union, a week before the results are due to be announced.
Gerard Coyne is regional secretary for the West Midlands, and is up against the sitting general secretary Len McCluskey, a prominent backer of Labour leader Jeremy Corbyn.
Unite has not confirmed why Mr Coyne has been suspended. The move coincides with the closing of the polls in the contest.
The result expected to be announced on 28 April.
Mr Coyne’s spokesperson confirmed he had been notified of his suspension.
During the campaign, Mr McCluskey has accused senior Labour figures such as Tom Watson of “manufacturing division” and “living in a world of skullduggery, smear and plots”, which has had the effect of framing the Unite contest around backing for Jeremy Corbyn’s leadership.
The union's acting regional secretary reportedly emailed local branches this afternoon, to tell them Mr Coyne had been relieved from his duties.
The email said the suspension was “pending investigation into certain issues which have arisen”.
A spokesperson for Unite could not confirm whether Mr Coyne had been suspended, and said that even if he had been, details could be revealed because “we do not comment on internal staffing matters”.
Mr McCluskey is favourite to win the election, remaining as general secretary for a third term.
There are three candidates for the post of general secretary - Mr McCluskey, Mr Coyne and grassroots member Ian Allinson.
The campaign has been bitter, running for several weeks, with personal and policy attacks from all sides.
Mr Coyne has criticised Mr McCluskey's strong support for Labour leader Jeremy Corbyn, accusing the union of becoming too political under his leadership.
Mr McCluskey has hit back, saying it made sense for Labour's biggest union affiliate to be close to the party.
Mr Coyne was criticised by Mr McCluskey for being too close to a number of Labour MPs in the West Midlands who opposed Mr Corbyn's leadership.
Although he has been suspended from his post as regional secretary, he remains a Unite member, so his supporters say he could still become general secretary if he wins.
It is believed that the ballot papers were being verified on Thursday but actual counting will not start until Friday.
The email sent to Unite staff and members in the West Midlands said: "This is to advise that Gerard Coyne has been suspended from his duties as regional secretary pending an investigation into certain issues which have arisen.
"The investigation is, of course, being conducted under procedure, and it should not be assumed that any offence has necessarily been committed.
"You will appreciate that it is not possible to comment further on this matter."