WASHINGTON — Republicans fired back at Warren Buffett after the billionaire investor argued in a newspaper opinion piece that the mega-rich in the United States are “coddled” by the tax code.

The country’s wealthiest citizens pay considerably less taxes, as a percentage of income, than the poor and middle class, Buffett said in a column published Monday in The New York Times.

“My friends and I have been coddled long enough by a billionaire-friendly Congress,” Buffett wrote. “It’s time for our government to get serious about shared sacrifice.”

Republicans responded with a series of Twitter messages questioning Buffett’s sincerity.

“For tax-raising advocates like Warren Buffett, I am sure Treasury would take a voluntary payment for deficit reduction,” Sen. John Cornyn, R-Texas, wrote in a tweet.

“If Warren Buffett wants to pay more taxes and send more of his money to Washington, why doesn’t he just do it?” tweeted Brad Dayspring, a spokesman for House Majority Leader Eric Cantor, R-Va., who has led the push against tax increases to help reduce budget deficits.

On the campaign trail in South Carolina, presidential hopeful Rep. Michele Bachmann, R-Minn., voiced a similar thought.

“We do believe, unlike Warren Buffett, that taxes are high enough already,” she said. “I have a suggestion: Mr. Buffett, write a big check today.”

This is not the first time that Buffett, a friend of and donor to President Obama, has used his personal tax bill – and those of his employees – to make the case that super-wealthy Americans are undertaxed.

In 2007, Buffett raised the issue at a fundraiser for then-Sen. Hillary Rodham Clinton, arguing that secretaries pay higher tax rates than their millionaire bosses and offering to pay $1 million to anyone who could prove him wrong.

This time, Buffett’s words come as a bipartisan committee of 12 members of Congress sets out to trim the federal budget gap by $1.5 trillion over 10 years, with the growing national debt becoming a central issue as the 2012 presidential race heats up.

In a Monday interview with PBS’ Charlie Rose, Buffett said the op-ed was aimed at that group known as the “supercommittee.”

“If I could pick 12 readers for it, they’re the ones,” Buffett said.

Buffett rejected the claim that raising taxes to cut U.S. deficits will kill jobs, arguing that the country had higher taxes between 1980 and 2000 and “nearly 40 million jobs were added.”

“You know what’s happened since then: lower tax rates and far lower job creation,” he said.

On Tuesday, Obama took Buffett’s op-ed on the campaign trail, citing it in town halls as he traveled through Minnesota and Iowa. As Obama was touting the Buffett piece, conservatives set out to debunk it.

“Apart for misstating his tax burden, Buffett fails to call for significant reforms in Social Security and Medicare that could reduce federal spending, and he downplays the role taxation plays in investment decisions,” wrote Mike Brownfield, the assistant director of strategic communications at the Heritage Foundation, a conservative think tank in Washington.

“A billionaire calling for more taxes might make great political theater, but there’s more to the story than Buffett – and Obama – would have you believe.”