Labour Party members should be given a say on who gets to stand for the party's leadership, Unite boss Len McCluskey has said.
Mr McCluskey, whose union is Labour's biggest donor, said MPs and MEPs should not have the exclusive right to determine who gets on the leadership ballot in future.
His intervention may be seen as a desire to boost the left's influence in Labour, and comes ahead of a party conference where Jeremy Corbyn's allies could attempt to change the rules to make it easier to get favoured candidates on the ballot.
The prospect of a big row over the so-called "McDonnell amendment", which would allow candidates to stand for the leadership with the support of fewer MPs, appears to have receded.
But discussing the proposed change, which would lower the threshold required to get on the ballot from 15% of MPs and MEPs to 5%, Mr McCluskey told Pienaar's Politics on BBC Radio 5 Live: "I'm not so sure about lowering the MPs but I do believe we should have ... "
He went on: "What I believe is that we should look at the democratic processes. The Labour Party is now the largest political party in Europe and we need to therefore look at that, the idea that it is only MPs that decide who goes on a ballot paper, I think is wrong, and I'd like to widen the franchise."
Asked if he would back the amendment, he replied: "We will have to see whether or not it comes up at the conference but what I am in favour of is Jeremy's belief that we should have an open democratic party."
Last month shadow chancellor John McDonnell said the "heat is off" on the amendment drawn up in his name as the mood towards the left wing of the party has changed among MPs after Mr Corbyn greatly outperformed expectations in the general election.