Former Health Services Union (HSU) national president Michael Williamson has arrived at Sydney's Maroubra Police Station.
He is expected to be charged later in the day over his involvement in the HSU scandal, ABC reports.
Mr Williamson walked in with one other person, presumed to be his lawyer, and plain clothed police stood by outside.
It's the first he has been seen since July, when he quit as national present of the union by text message.
A police spokesman told AAP they could not confirm if Mr Williamson would be charged on Thursday.
An officer at Maroubra later confirmed Mr Williamson had entered the station, and told AAP "a lot of suits had been walking in and out".
Just after 8am (AEST) police confirmed in a statement that a 59-year-old man had been arrested at the station for attempting to hinder investigations into fraud against, and corruption within the HSU.
"Detectives anticipate charging him with a number of offences relating to hindering investigations, including recruiting a person to engage in criminal activity and (being an) officer of an organisation publishing false statements," the statement said.
A media briefing will be held at Maroubra at 10am.
Mr Williamson stood aside in September last year amid allegations of misuse of union funds investigated by Fair Work Australia and police.
His resignation by text message to a senior union official in July came in response to the leaking of a report by barrister Ian Temby QC.
Mr Temby found more than $20 million of questionable payments were made to suppliers without any form of tendering or contract.
His report into the HSU East branch revealed extravagant salaries, excessive credit cards claims, misuse of union funds, nepotism and poor governance.
Mr Williamson was the president of the Australian Labor Party at the time of the alleged activities.
The HSU scandal has embroiled suspended Labor MP Craig Thomson, a former national secretary of the HSU and made matters difficult for the federal government.