"In recent months, my professional and personal reputation has been repeatedly questioned through the media," he told Fairfax Media. "After consultation with my family and medical professionals, I came to the conclusion that it is no longer in my best interest to remain in such an environment and I have decided to pursue options outside of media and government." Senator Cash's media adviser, David De Garis, resigned in October after admitting he told the media the police were about to raid the offices of the Australian Workers Union as part of an investigation into donations. He has not publicly revealed who told him the raids were about to occur. But suspicion fell on Mr Lee after it emerged he knew search warrants were being sought as part of the Registered Organisation Commission's investigation into donations the AWU made 10 years ago to activist group GetUp! While Mr Lee worked for the ombudsman, he had at the time also been assisting the ROC with its media relations.

It later emerged that Mr Lee had been hired by Senator Cash - before the raids took place - to replace Mr De Garis as her media adviser. That plan was scrapped as a result of the controversy and he stayed with the ombudsman. But Mr Lee has denied he was the source of the leak. Loading Replay Replay video Play video Play video Fair Work Ombudsman Natalie James told a Senate estimates hearing last year Mr Lee had no contact with anyone outside the agency before the raids started. Fair Work Ombudsman Natalie James. Credit:James Brickwood

"He had no conversations with anyone outside of the agency about these matters until he started receiving calls, after the searches were being executed, from journalists wanting comment. He was attending a private appointment at this time. His responses to those journalists were that he didn't know and he would need to get back to them," she said. However it has emerged through freedom of information documents that he did speak with Mr De Garis that evening, after the raids were executed. Senator Cash's office has shed a number of other staff members in recent months, including her chief of staff and a second media adviser. Labor's workplace spokesman Brendan O'Connor said the government had to answer all questions about who was involved in the leak. “Which resignations or sackings are linked to the AFP investigation into the ROC leak? As long as questions remain unanswered, this farce will continue," he said.