Sen. Marco Rubio (R-FL) on Monday called for the non-existent commissioner of the Internal Revenue Service to resign over the agency's targeting of tea party groups.

"[I]t is clear the IRS cannot operate with even a shred of the American people’s confidence under the current leadership," he wrote in a letter to Treasury Secretary Jack Lew. "Therefore, I strongly urge that you and President Obama demand the IRS Commissioner’s resignation, effectively immediately. No government agency that has behaved in such a manner can possibly instill any faith and respect from the American public."

Several publications were quick to point out that the IRS Commissioner in question, Douglas Shulman, ended his five-year term in November 2012. IRS Deputy Commissioner Steven Miller has acted as the head of the agency pending President Barack Obama's nomination of a successor.

Tea party groups complained of excessive IRS questioning in 2012 after they voluntarily applied for tax-exempt status under section 501(c)(4) of the federal tax code. The so-called social welfare organizations are prohibited from engaging in partisan campaign activity, but Republican strategists like Karl Rove have used the nonprofits to fund political campaigns without disclosing donors. Democrats have also made use of social welfare nonprofits to a lesser extent.

At the time, some hailed the news as the IRS "doing its job."

"These tea party groups, a lot of their material makes them look and sound like a political party," Marcus S. Owens, a tax lawyer, explained to the Associated Press in 2012. "I think the IRS is trying to get behind the rhetoric and figure out whether they are, at their core: a political party."

The IRS admitted on Friday that it subjected tea party groups to extra scrutiny and described such targeting as "inappropriate." Republicans quickly made political hay out of the news, accusing the Obama administration of intimidating its opponents, even though Shulman was nominated by George W. Bush.

"The American people deserve answers about how such seemingly unconstitutional and potentially criminal behavior could occur, and who else was aware of it throughout the Administration," Rubio said.