Labour's ruling National Executive Committee (NEC) agreed to bring in a new code of conduct for party elections to prevent disputes over their handling becoming public.
The move comes after allegations that running totals of how votes were being cast in last year's elections to the NEC, and the recent battle to become Labour's leader in Wales, were leaked to national party bosses during the ballot, enabling pro-Blair candidates to maximise their votes.
Four left-wing members of the NEC voted against the reforms. Liz Davies, one of the four, said: "There are several stipulations which are wholly unnecessary restrictions on the democratic rights of Labour Party members. This is part of the drive to silence dissent."
The left-wingers also criticised the NEC's decision yesterday to suspend the constituency party in Newark, Nottinghamshire, after the conviction last week of Fiona Jones for making false declarations on her general election expenses.
Mark Seddon, a left-wing NEC member, said: "It is not a good idea to close down the Newark Labour Party. The whistleblowers should not be disciplined."
But Vic Hall, secretary of the Newark Labour Party until its suspension, said: "This is the news we were waiting for. It means the party can move forward and mount an effective campaign in the elections."