(CNN) - The two leaders of the Republican Governors Association called for the appointment of a special prosecutor Tuesday to investigate any legal wrongdoing within the Internal Revenue Service.
Gov. Bobby Jindal of Louisiana and Gov. Scott Walker of Wisconsin - who both are considered potential candidates for the 2016 GOP presidential nomination - wrote in a letter to President Barack Obama the recent revelation the IRS was applying extra scrutiny to conservative groups applying for tax exempt status amounted to a "witch hunt to prevent Americans from exercising their First Amendment rights."
"The First Amendment gives Americans the ability to freely express their opinions regardless of their political beliefs," the two governors wrote. "The actions of the IRS are an attempt to gag the voices of Americans who may disagree with the policies and left-leaning ideology of your administration. Quite frankly, this is un-American."
On Friday, the Republican-led House Ways and Means Committee will convene the first formal hearing on the IRS practice, with the agency's commissioner and inspector general set to testify.
Other committees, including in the Democrat-led Senate, have also vowed to look into the IRS's admission it targeted tea party organizations and other groups focused on government spending. The tax agency said its motivations were not political.
Jindal and Walker are the first high-profile elected officials to formally ask Obama to appoint a special prosecutor, who would be independent of the federal government to avoid conflicts of interest.
Special prosecutors have been used in the past to probe high level government officials who are accused of wrongdoing.
On Monday, Obama vowed to hold IRS employees responsible if the charges of political targeting turn out to be true.
"If in fact IRS personnel engaged in the kind of practices that have been reported on and were intentionally targeting conservative groups, then that's outrageous. And there's no place for it," Obama said.
"They have to be held fully accountable," Obama continued. "Because the IRS as an independent agency requires absolute integrity, and people have to have confidence that they're ... applying the laws in a nonpartisan way."