Buffett backs a surtax on the wealthy.
"It's the wrong policy to have," Buffett said on Bloomberg Television Monday. "He's not going to pay more than the law requires, and I don't fault him for that in the least. But I do fault a law that allows him and me earning enormous sums to pay overall federal taxes at a rate that's about half what the average person in my office pays."
Buffett, chairman and chief executive officer of Berkshire Hathaway Inc., supports President Barack Obama's call to raise taxes on the wealthiest Americans to help close the budget deficit.
Romney agreed under pressure from his GOP rivals to release his 2010 tax return Tuesday, after saying in a recent debate he pays about 15 percent. Romney co-founded Boston-based private-equity firm Bain Capital.
A filing with the Federal Election Commission last year indicated Romney was worth between $190 million and $250 million, the former Massachusetts governor's campaign said.
"He makes his money the same way I make my money," said Buffett, 81. "He makes money by moving around big bucks, not by straining his back or going to work and cleaning toilets or whatever it may be. He makes it shoving around money. I make it shoving around money."
With rival Newt Gingrich's win in South Carolina and surge in recent polls, Buffet said the events of the past 10 days were more about "Romney losing ground … than it was Newt gaining, although Newt made the most of it."
In the end, whether a candidate releases his tax returns shouldn't decide an election, he said.
"[Romney] should have done better on it, and it hurt him a lot, I think," Buffett said, "but I don't think that is the determining factor in who should be president."