Labor has seized on claims that Attorney-General George Brandis used taxpayer funds to attend a wedding two years ago, saying the incident shows the Senator is "not fit" to draft a new code of conduct for ministers.
Senator Brandis has confirmed he claimed nearly $1,700 on flights, accommodation and a hire car to attend the wedding of radio presenter Michael Smith, but says it was primarily for work purposes.
Following Sunday's newspaper reports, he wrote a letter to the Department of Finance with a cheque for the costs, saying he would pay them to "resolve any uncertainty" about the issue.
Fellow Coalition frontbencher Barnaby Joyce was also reported to have used taxpayer funds to attend the wedding but says the idea he claimed thousands of dollars is "just wrong".
Shadow attorney-general Mark Dreyfus says the incident shows Senator Brandis is "not the person for the job" of developing a new code of conduct.
In a statement, Mr Dreyfus says Prime Minister Tony Abbott should find another minister to do the task.
"The fact that Senator Brandis - after initially trying to defend his actions today - has now scrambled to repay the money when it was clear that no one was buying his excuses, clearly demonstrates the breach," Mr Dreyfus said in the statement.
"Mistakes are made from time to time by members of all sides of politics in claiming travel entitlements, and in such circumstances timely repayment is the appropriate response.
"However, Senator Brandis has spent years in opposition demanding strict adherence to travel entitlements, and has never hesitated to call in the Federal Police for any imagined wrong.
"Senator Brandis has demanded that others meet standards that he is not prepared to meet himself."
Smith has defended the actions of the politicians on his website and said he and his wife paid for the politicians' limousine to the wedding.
He says any expense claims were justified because both men engaged with journalists at the wedding and their attendance at the celebration "did not demur in any way from their paid elected role as prominent federal parliamentarians".
According to the federal Department of Finance and Deregulation's entitlements handbook, expenses for official business such as "meetings of a government advisory committee or taskforce" or "functions representing a minister of presiding officer" are allowed for.
Meetings with journalists and other members of the media are not sanctioned under the handbook's guidelines.