Labour's former deputy leader Lord Prescott today said it was "time for change" in the party's relations with the trade unions.
Party leader Ed Miliband is expected to clash with union bosses over his proposals for changes which would reduce their voting power at the annual conference.
The issue is expected to come to a head at next month's conference in Liverpool, where unions are likely to resist any move to reform the party's democratic structures, which currently give them 50% of the vote.
Lord Prescott today said that rank-and-file activists felt that the current arrangements were "loaded" against them and in favour of the unions. Mr Miliband's proposals were intended to produce "a modern party in modern circumstances".
Lord Prescott told BBC1's Andrew Marr Show: "There is a feeling in the constituencies that perhaps the power of the trade unions has been loaded a bit against the constituencies.
"When I stood for treasurer, I got 63% of the actual votes of the constituencies and hardly anything from the unions because three or four general secretaries decided I wasn't going to be the one and therefore didn't ballot their members, so it's time for change."
Lord Prescott compared Mr Miliband's proposed changes to the "one member one vote" system which former leader John Smith forced through in 1993 to remove the power of the union block vote.
"I think the debate should go on," said the former deputy leader. "Ed will have to put these arguments forward and there may be resistance to them - there was against one member one vote - and then the conference will have to make a decision.
"These are constitutional changes that Ed is talking about. They are always controversial. But he is a man of reform. He has only been in the job for 12 months, but he has made some headway."