An adviser to Opposition Leader Bill Shorten has quit over a Facebook post in which he appears with a painted blackface.
Steve Michelson, who has advised Mr Shorten for six years on stakeholder relations, had been considering a parliamentary career.
The Facebook photo was taken at a 2007 party, but is understood to have been shopped around by Mr Michelson's Labor factional opponents in recent months.
A spokesman for Mr Shorten said the conduct was "clearly unacceptable and out of character for Mr Michelson, who was a valued and diligent staff member".
Mr Michelson has admitted the behaviour was inappropriate.