Labor is demanding Malcolm Turnbull explain to the public why he waited so long to force the departure of Mal Brough from the frontbench, timing the announcement just minutes after junior minister Jamie Briggs quit in disgrace.

Mr Briggs resigned on Tuesday for acting unprofessionally towards a female public servant he invited out to late-night drinks at a bar in Hong Kong, where he was on an official visit with his Chief of Staff Stuart Eaton late last month.

Labor has written to the former minister and the public service commissioner seeking further details of the incidents and reassurances that there will be no adverse consequences for the public servant involved.