Acting Prime Minister Warren Truss has warned all members of parliament to exercise extreme caution with their expense claims.

Coalition frontbenchers George Brandis and Barnaby Joyce have both been forced to repay parliamentary expenses they claimed to attend the 2011 wedding of former 2UE shock jock Michael Smith.

Mr Truss says the rules governing expense claims are not as clear as they should be.

But he says MPs must always exercise extreme caution remembering that "people have worked very hard to pay the taxes that fund those benefits".

"People have a right to know that the money that members of parliament use is used correctly," he told reporters in Brisbane on Tuesday.

He said the media had a right to closely scrutinise such claims.

But he added: "Clearly there's a lot of work being done at the present time by people who feel that this might sell a few newspapers."