The fight to lead Britain's biggest trade union has grown increasingly bitter, with current leader Len McCluskey accused by a rival of being Jeremy Corbyn's "puppet master".
Gerard Coyne, who is challenging Mr McCluskey in the union's leadership elections, told The Observer that the Unite boss was meddling too much in Westminster politics at the expense of the union's membership.
"I just don't think that ever again the general secretary should be the puppet master of the leader of the Labour Party," he said in an interview with the newspaper.
"There is an opportunity for change, for a fresh start, for members to get their union back."
There are many in Labour who agree with Mr Coyne and see his candidacy as a chance to break an alliance between Mr Coybyn and the union's leadership.
Mr McCluskey has repeatedly backed the Labour leader against his challengers, throwing the union's weight behind him.
But he says that support is the decision of the union's executive and members, not a personal move.
Mr McCluskey's five-year term is due to end in 2018, but he opted to bring the election forward by a year to spring.