The prime minister says Labor should stop attacking companies over industrial relations following awkward revelations about Kevin Rudd's wife's company.
Almost 60 staff at one of Therese Rein's job placement companies were underpaid after they were moved on to common law contracts that stripped award conditions in return for just 45 cents extra an hour.
The opposition leader said his wife had made an honest mistake and had compensated the workers as soon as the error was spotted.
Mr Howard declined to criticise Ms Rein directly, saying the matter was being investigated by the Office of Workplace Services.
But he said the Labor Party should stop attacking businesses like the Lilac City motel in Goulburn, which was criticised this week for introducing a new Australian Workplace Agreement (AWA).
Mr Howard said the motel owners had received hate emails from as far away as Norway after Labor's industrial relations spokeswoman Julia Gillard leapt on a newspaper report about the AWA without checking the facts.
"We did not start this. We are not making wild accusations about Mr Rudd's wife," Mr Howard told Southern Cross Broadcasting in Melbourne today.
"We are making very strong accusations about the behaviour of Mr Rudd and Ms Gillard towards other companies, some of whom have made honest mistakes.
"Now, if we're not to have a double standard, an honest mistake made by one company is as good and as excusable as an honest mistake made by another company.
"We've had too much of this use of parliamentary privilege to attack the reputations of hardworking businessmen and women.
"Vulnerable small businesses have their reputations trashed all across the country and there's not so much as an apology."