The Federal Opposition says Speaker Bronwyn Bishop must produce proof she did not misuse her entitlements to travel to a colleague's wedding.

The Prime Minister has put Mrs Bishop "on probation" as the Department of Finance investigates her use of charter flights, one of which was to attend a Liberal Party function.

Mrs Bishop claimed $600 in flights to Albury in 2006, saying she was travelling on business related to her role on the Parliament's Family and Human Services Committee.

She then went to Wangaratta to attend Liberal frontbencher Sophie Mirabella's wedding.

Labor frontbencher Kate Ellis was also on the committee and said there was no record of any business in Albury that weekend.

"I struggle to think of any reason why the chair of the committee Bronwyn Bishop would be there on committee business," she said.

Ms Ellis said Mrs Bishop would have had to ask the committee for permission to travel individually, and that would have been recorded.

"Of course we've seen her press conferences, we've seen the ducking and weaving, but what we haven't seen is the black and white proof," she said. "It should exist."

Mrs Bishop's office said it was common for committee chairs to conduct their own investigations as part of committee inquiries.

But Liberal Party frontbencher Michaelia Cash said Mrs Bishop should repay the money if it was claimed in error.

"It's either in entitlements or it's not in entitlements, that's how I work," she said.

"If something's not in entitlements, mistakes can be made, you should pay the money back, with the appropriate penalty."