Cain's accountant contested the notice and penalty, and the lien was eventually withdrawn in 2008.

Gordon said that the case was illustrative of a broken and bureaucratic taxation process.

"The experience serves as an example of how broken our federal and state bureaucracies are with respect to the collection of revenue," Gordon said in a statement. "The entire process is driven by automated letters generated in response to deadlines."

Cain's campaign has caught fire on the back of his 9-9-9 taxation proposal, which would replace the current federal tax code with 9 percent flat taxes on personal income, corporate profits, and sales. In a New York Times/CBS poll released Tuesday, Cain led the Republican field.