Bronwyn Bishop is under pressure to fully explain what "official business" she was undertaking when she charged taxpayers for attending Sophie Mirabella's wedding after a fellow committee member questioned the Speaker's version of events.

Fairfax Media revealed last week that the Speaker, already on "probation" for use of her expenses, claimed $600 in return flights to Albury on a day that coincided with the wedding of her colleague, then-MP Sophie Mirabella.

Despite Prime Minister Tony Abbott having previously repaid more than $1000 entitlements claimed to attend the same wedding, Mrs Bishop has so far refused to repay the money.