Opposition leader Tony Abbott failed to declare a new mortgage he took out on his family home shortly after the last election - and has come under attack from Labor.
Mr Abbott borrowed $170,000 against his family home in Forestville, NSW in April 2008, four months after the Howard government lost office, News Ltd reported on Wednesday.
Abbott may be in breach of parliamentary rules covering pecuniary interests after he failed to declare the loans to parliament for almost two years.
Parliament requires all MPs to register any changes to interests, benefits or liabilities within 28 days.
Labor MP Jim Turnour rounded on Abbott and said it shows Abbott's able to forget about his mortgage, while working families think about their repayments all the time.
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But a spokeswoman for Mr Abbott said the failure to declare the loan was an oversight.
Opposition finance spokesman Andrew Robb said it was a "simple mistake" and accused Labor of stooping to muckraking.
"There's no reason why he wouldn't disclose it, unless he's overlooked it really," he told reporters in Canberra.
