The Jobs Minister has been under pressure over her role in a federal police raid conducted on AWU offices in Melbourne in October, details of which were leaked to the media in advance. She was previously issued a subpoena in March but this was later set aside. Senator Cash's former staffer David De Garis - who has also been ordered to give evidence - took the blame for tipping off journalists about the police raids and subsequently resigned. Former Fair Work Ombudsman media officer Mark Lee and Registered Organisations Commission official Chris Enright have also been ordered to give evidence in court on August 1. Employment Minister Michaelia Cash during a Senate estimates hearing earlier this week. Credit:Dominic Lorrimer

AWU national secretary Daniel Walton said it was vital for the court to hear evidence from witnesses whom the union believes are relevant to the case. "That is why we sought subpoenas," Mr Walton said. "If we are to understand exactly what happened then we believe the testimony of these individuals is critical. "We have long believed last year’s raid – and the investigation itself – to be unlawful." Senator Cash says she was unaware her office had tipped off journalists about the raids. On Wednesday she again instructed her lawyers to apply to have this round of subpoenas set aside. A previous attempt to stop a subpoena for communications between her office and the Registered Organisations Commission mostly failed. "The person who has questions to answer is the former head of the AWU, Bill Shorten," Senator Cash argued on Wednesday. "Today is just another effort by the union movement to protect Bill Shorten."

The AWU has taken the Registered Organisations Commission to court to throw out an investigation into donations the union made to activist group GetUp! when Mr Shorten was national secretary. The AFP is conducting an investigation into the leaks, which resulted in video of the raids appearing on the evening news. At Senate estimates on Tuesday, Senator Cash declined to answer questions about the matter, citing public interest immunity, and prompting Labor to accuse her of a "cover up". Shadow employment minister Brendan O'Connor said Senator Cash should answer questions before the Senate or be sacked by Prime Minister Malcolm Turnbull. As a minister, Senator Cash was accountable for the conduct of her office but was “hiding” behind public interest immunity. "She should have taken responsibility for the conduct of her office seven months ago and resigned," Mr O'Connor said. "It is untenable for this to continue. “This is not just about a crime - it is also about ministerial responsibility”.

In a farcical scene earlier this year, Senator Cash was shielded from the cameras by a whiteboard as she made her way to a Senate estimates hearing in Parliament House. On Wednesday she said she had "nothing to do" with that stunt and it was solely instigated by Parliament House security. Mr Turnbull has so far stood by his minister. The Australian Council of Trade Unions Secretary Sally McManus said Minister’s efforts to avoid answering questions about what she knew about the police raid was "regrettable". “It is extraordinary that a Minister would have to be subpoenaed to speak about a vital matter of national importance and even more extraordinary that she would try and avoid the actions of a court trying to get to the bottom of the matter," she said. “We, like the rest of Australia, look forward to finally hearing the truth on this matter.”