The Australian Taxation Office has cautioned people claiming work-related expenses to ensure they've done their paperwork.
Australia's tax commissioner Chris Jordan says a recent random check of work-related expenses had turned up a "very large amount" of wrongful claims.
Mr Jordan told a Senate estimates hearing on Wednesday in one case a man claimed $20,000 for tools, arguing he bought them with cash from gambling winnings which he kept at home and not in a bank account.
However, the taxpayer could not even show officials the tools, saying he had sold them on to someone else, and claimed he had spent the money from the sale.
"Sometimes people literally just make up deductions," Mr Jordan said.
In another case, a taxpayer claimed 100 per cent of the cost of a holiday as an "overseas study tour".
Mr Jordan said that of all the cases that had been taken to the Administrative Appeals Tribunal by taxpayers over their work-related expense claims being knocked back, the tax office had won 100 per cent.
"You've got to actually spend the money and not be reimbursed, it's got to be related to your work, and you've got to keep a record of it," he said.