Former Fair Work Commission vice-president Michael Lawler has withdrawn legal action against the Employment Minister, just days after claiming he was unfairly treated during an investigation into alleged misconduct during his time in office.

The investigation was commissioned after serious criticism was levelled at Mr Lawler for supporting his partner and ex-union boss Kathy Jackson, as she battled fraud allegations from her time at the helm of the Health Services Union.

He was on nine months' sick leave, and still receiving his full $430,000 annual salary.

Mr Lawler quit his position in March, less than 24 hours before he was due to respond to the investigation's findings and a fortnight before Senator Cash tabled it in Parliament.

Court documents obtained by the ABC showed Mr Lawler was calling for a judicial review into the decision to launch the investigation, the conduct of Senator Cash during the course of the investigation, and the decision to table the final report despite Mr Lawler having already resigned from his position.

He also admitted that participating in an episode of the ABC's Four Corners alongside Ms Jackson was an "error of judgment".

A Notice of Discontinuance was filed in the Federal Court on Tuesday.

Last week, Senator Cash's office said Mr Lawler's application was "misconceived" and would be opposed by the Commonwealth.