Former home secretary Alan Johnson - an ex-union leader - warned against "petty retribution" in the wake of Ed Miliband's party reform pledge.
"We can no longer go on living the lie with these millions of people signed up as levy-paying members to the Labour Party, and treated as if they were members," Mr Johnson told BBC Radio 4's The World At One.
"I call them the ghosts in the machine. That is bad for the party, it is bad for the trade unions."
The former Communication Workers Union chief added, "I just hope this is not a piece of petty retribution by a trade union."
More top news
Average household incomes have returned to around the levels they were at before the financial crisis hit, new analysis indicates.
Figures uncovered by a Freedom of Information request reveal one university leader received £623,000 in 2013/14.
Tens of thousands of students are not achieving their potential in state schools, a highly-critical Ofsted report has said.