Prime Minister David Cameron has branded comedian Jimmy Carr "morally wrong" for seeking to avoid taxes.
Reports of Carr's tax arrangements suggest he is undertaking "straightforward tax avoidance", said the Prime Minister.
He said it was unfair on the people who pay to watch the comic perform that he is not paying his taxes like they do.
"I think some of these schemes - and I think particularly of the Jimmy Carr scheme - I have had time to read about and I just think this is completely wrong," he told ITV during a round of TV interviews in Mexico, where he is attending a G20 summit.
"People work hard, they pay their taxes, they save up to go to one of his shows... He is taking the money from those tickets and he, as far as I can see, is putting all of that into some very dodgy tax-avoiding schemes.
"That is wrong. There is nothing wrong with people planning their tax affairs to invest in their pension and plan for their retirement - that sort of tax management is fine.
"But some of these schemes we have seen are, quite frankly, morally wrong."
But Labour leader Ed Miliband criticised Mr Cameron's comments.
"I'm not in favour of tax avoidance obviously," he said.
"But I don't think it's for politicians to lecture people about morality. I think what politicians need to do is, if the wrong thing's happening, change the law to prevent that tax avoidance happening."
Carr is said to have used an aggressive, legal, tax-avoidance scheme which enables members to pay income tax rates as low as 1%.
The comic, who has famously lampooned fat cat bankers, reportedly protects some £3.3m a year by channelling cash through Jersey-based company K2.
He spoke out over the claims during a show in Tunbridge Wells, Kent, on Tuesday, reportedly saying: "I pay what I have to and not a penny more."
Carr is said to be one of more than 1,000 beneficiaries who shelter some £168m from the taxman each year using K2. HM Revenue and Customs (HMRC) said the K2 scheme was already under investigation.