Defence Minister David Johnston's office is in chaos, with two staff members shown the door as the Defence Department launched an investigation into a damaging leak of the minister's expense receipts.

The departure of the two staff members came on the morning that leaked receipts revealing restaurant bills racked up by Senator Johnston and his chief-of-staff Sean Costello were published in the media.

Fairfax Media understands that no accusations relating to the leak were made against the two staff members, media adviser Mark Dodd and an international policy adviser, whom Fairfax Media is not naming.

Nor were they given any reason why they were being asked to leave, it is understood.