The revelations by The Independent - on the eve of the TUC's annual conference in Brighton - come on the same day that the GMB, one of the Labour Party's leading affiliates, launched a campaign against companies who snooped on their workers.
Mr Edmonds, once offered a peerage by Tony Blair, was among the most articulate advocates on behalf of working people, but was famous for calling directors of major companies "greedy bastards" for taking large pay rises.
One of the GMB employees allegedly under scrutiny was Tom Condon, once industrial editor of The Sun newspaper, who worked as Mr Edmonds' spin doctor.
Mr Condon, who was dismissed for "unsatisfactory performance" in December 1998 after a year with the union, criticised Mr Edmonds for presiding over a property deal which lost the union £6m.
Mr Condon said yesterday: "I am obviously pleased that the union is now going to investigate how John Edmonds wasted so much of the members' hard-earned cash in following me around for three months. But the question it should really address is why?"
Contacted by The Independent yesterday, Mr Edmonds would only say: "I don't want to say anything about it. I don't think it would be helpful to comment."
In a letter to the GMB's president, Mary Turner, the union's acting general secretary, Paul Kenny, is understood to have called for an auditor's inquiry into the snooping allegations against Mr Edmonds.
Mr Kenny told the president that he could find no authority for the alleged payments to the private detective agency or copies of the reports they supplied.
Yesterday, the executive of the union endorsed the call for an auditor's investigation into the allegations, and called for copies of any documents produced by the detective agency, which is understood to be based near Farringdon.
Mr Kenny's letter points out that any documents from the agency should have been given to the union when Mr Edmonds retired in June 2003. The acting general secretary said in his letter that it was important that such an issue should be addressed by the union so that employees could have confidence in the organisation's internal procedures.
As the letter was read out to the 70-strong meeting of the executive in Brighton, some of its members gasped at its implications for the union's reputation. Although the GMB has had a name for taking on "bad bosses", it has come under constant fire for the way it treats its own staff.
One insider estimates that the GMB has spent up to £4m in recent years fending off allegations of sexual harassment and bullying against some of its most senior officials.
One source close to the union said it had been involved in more than 60 employment tribunal cases over the past six years involving its own employees.
A spokesperson for the union said: "The central executive council has asked auditors to establish whether any expenditure was incurred on this matter and who authorised it, and for what purpose."Reuse content