Labor leader Bill Shorten said Senator Malarndirri McCarthy had taken "the right of course of action" in referring herself to the Independent Parliamentary Expenses Authority over queries about her travel.
"We'll see what they say," he told reporters on Saturday.
The Northern Territory senator is in hot water over questions about $100,000 she has spent on mostly business flights, according to The Courier Mail.
Ms McCarthy also apparently spent at least 120 nights in Sydney since being elected to represent the NT in the Senate in 2016.
A spokeswoman for the senator said her medical issue "necessitates a break in travel" and that she has been undertaking medical treatment with a long-term specialist in Sydney.
But on the issue of business flights she said in a statement: "I am absolutely confident that all travel has been undertaken within the rules, but to remove any doubt, I have immediately asked the Independent Parliamentary Expenses Authority."
Ms McCarthy is expected to retain an NT seat in the Senate for Labor.
