Speaking to a reporter with Bloomberg TV on Monday, billionaire investor Warren Buffett upped his challenge to congressional Republicans and even managed to work in a slap at presidential candidate Mitt Romney, saying that he would donate 15 percent of his annual income if just 10 percent of the Congress would do the same.

That's not likely to happen any time soon, which is precisely why he made the pledge.

Buffett had previously offered to match Republicans' donations to the national deficit, as part of a war of words with Senate Minority Leader Mitch McConnell (R-KY). McConnell had previously suggested that Buffett should open his checkbook to pay down the deficit, instead of advocate for a more progressive tax policy that requires wealthy people to pay more of the income in taxes.

Monday's challenge was also a slap at Romney, who recently revealed that he pays roughly 15 percent of his annual income in taxes. "That's exactly what I expected," Buffett said. "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."

He added that Romney's recent loss in the South Carolina primary was not due to former House Speaker Newt Gingrich (R-GA) gaining momentum so much as Romney losing it. "I think Romney hurt himself," he explained, talking about the former Massachusetts governor's reluctance to release his tax returns. "I think it was more Romney losing ground than Newt gaining."

The billionaire added that he would ultimately like to see wealthy people paying a higher percentage of their income in taxes -- something that President Obama has repeatedly proposed, drawing ire from the worlds of banking and finance, which have largely broken for Romney as their favored candidate in 2012.

Romney has since said he would release his tax returns in the coming days.

This video is from Bloomberg TV, broadcast Monday, Jan. 23, 2012.