Senator Michaelia Cash's chief of staff Ben Davies was the source of a controversial leak to the media about imminent police raids at Australian Workers' Union offices.
David de Garis, a former media adviser to the Senator who admitted leaking those details to journalists, was ordered to name his source after a ruling by Federal Court Justice Mordecai Bromberg on Tuesday that it was in the interest of justice for the information to be revealed.
The union is taking legal action against the Registered Organisations Commission, arguing the federal police raids on the union's Melbourne and Sydney headquarters in October 2017 as part of a commission investigation were politically motivated and therefore unlawful.
The raids were carried out as part of an investigation by the commission into donations to activist group GetUp! totalling $100,000 from two divisions of the AWU going back to 2006.
Mr de Garis told the court on Monday that he first heard about the raids at some time between midday and 4.30pm on October 24.
The raids took place that day.
However, he refused to answer who told him of the raids.
“I respectfully decline to answer on the grounds it may incriminate me,” he told the court.
On Tuesday he revealed that the source was his former colleague Mr Davies.
Senator Cash will front court on Friday over her involvement in the raids.