The Australian Workers' Union (AWU) served legal documents to Michaelia Cash's former chief of staff Ben Davies on Monday, as part of its challenge of the police raids on its offices last year.
BuzzFeed News revealed last month that the union hired private investigators to track down Davies in order to serve him with a subpoena to produce documents and give evidence in the Federal Court.
Davies' lawyers told the ABC that hiring the investigators was unnecessary. They claim he does not have any information relevant to the case.
The AWU launched its Federal Court challenge after BuzzFeed News revealed that Cash's office tipped off the media about the October 24, 2017 raids by the Australian Federal Police (AFP) on its Sydney and Melbourne offices.
The raids were part of an investigation by the Turnbull government-established watchdog, the Registered Organisations Commission (ROC), into donations made by the union over a decade ago, when it was led by current Labor leader Bill Shorten.
Cash denied five times in Senate Estimates last year that her office had any involvement with the media leak, before announcing her senior media adviser David De Garis had claimed responsibility and resigned. In February a journalist claimed they had received a phone call from then justice minister Michael Keenan's office informing them of the raids before they took place.
The union has also issued Federal Court subpoenas to produce documents and give evidence to four other people: Cash, De Garis, former Fair Work Ombudsman media officer Mark Lee and ROC official Chris Enright.
To date, Cash has not challenged the subpoena, but has publicly indicated she instructed her taxpayer-funded lawyers to do so.
The case has been delayed until the AFP's investigation into the "unauthorised disclosure of government information" is complete. It is currently slated for trial in February 2019.
The AFP told Senate Estimates last month that the investigation is not officially complete, but that it has provided a full brief of evidence to the Commonwealth Director of Public Prosecutions.
Internal AFP documents published by BuzzFeed News revealed the leak investigation was given the same priority as the investigation into the "liking" of a porn tweet by minister Greg Hunt's Twitter account. That six-month investigation found the minister's account was not hacked.
At the time of publishing Davies' lawyers had not responded to questions from BuzzFeed News.
UPDATE: Apology to Mr Davies
On 23 October, 24 October and 13 November 2018 BuzzFeed Australia published articles by former BuzzFeed political journalist Alice Workman about a Federal Court case concerning the Australian Workers Union's (AWU) attempt to prevent the Registered Organisations Commission’s investigation into union donations to the Australian Labor Party and activist group GetUp. These articles reported allegations by the national secretary of the AWU, Daniel Walton, that the AWU had to engage private investigators to "track down" Ben Davies, former chief of staff to Minister Michaelia Cash, in order to serve him with a subpoena and had been unable to locate him as he had “disappeared” in order to conceal his whereabouts and avoid such investigators.
BuzzFeed accepts that the various allegations made by Mr Walton and the AWU against Mr Davies were untrue and without foundation.
Neither BuzzFeed nor Ms Workman contacted Mr Davies prior to publishing these allegations and we accept that he was unaware of any attempts by or on behalf of the AWU to contact him, had never sought to conceal his whereabouts and has never had any contact with private investigators. BuzzFeed further notes that Mr Davies' solicitors had approached the solicitors for the AWU, Maurice Blackburn, to accept service and refute Mr Walton's allegations on 26 October 2018.
BuzzFeed and Alice Workman apologise to Mr Davies for the hurt and embarrassment caused by the articles.