Former Health Services Union leader Kathy Jackson is facing dozens of fraud related charges and the prospect of a jail term over allegations she misappropriated hundreds of thousands of dollars of union funds.

Ms Jackson was charged on Wednesday via summons in NSW with 70 counts of obtaining property by deception and other fraud related offences.

She refused requests to be interviewed by Victorian detectives, despite rising to fame as a union whistleblower who had assisted police in investigating her former union colleagues.

Fairfax Media has confirmed some of Ms Jackson's closest former union allies have agreed to testify against her.