Cabinet minister Michaelia Cash says she was unaware her former chief of staff had been served with legal documents over raids on union offices.

The Australian Workers’ Union is pursuing Federal Court action over federal police raids on its offices in Sydney and Melbourne more than a year ago.

Senator Cash’s former chief of staff Ben Davies was on Monday served with a subpoena by AWU lawyers to give evidence in court and produce documents over the matter.

The raids were about a donation made by the AWU to activist group GetUp when Opposition Leader Bill Shorten headed up the union more than a decade ago.

During question time on Tuesday, Labor’s Murray Watt asked Senator Cash if she knew about the subpoena served on Mr Davies.

“You know more than me because I’ve only just been informed of that matter by you,” she told parliament.

“I have not discussed it with my former chief of staff.”

The small business minister challenged Mr Shorten to come clean over his knowledge of the donations.

“Maybe Mr Shorten ought to front up. The AWU, they can subpoena him because you can subpoena anyone,” Senator Cash said.

The raids drew scrutiny because journalists arrived at the offices before police after a tip-off from Senator Cash’s office.

The minister has consistently denied any knowledge of leaking from her office or being aware the raids were going to happen before they became public.

“Again here today we have Senator Cash telling the Senate she doesn’t know about media reports that her former chief of staff has been served,” Senator Watt said.

“Forgive me if I’m a little bit sceptical.”

Senator Cash was served with a subpoena earlier in the year but flagged her intention to have it set aside.

The court case is expected to start in February next year.

-AAP