Rep. Darrell Issa (R-Calif.) sent a letter to the Federal Election Committee (FEC) on Wednesday requesting documents he says are potentially related to “inappropriate coordination” between the independent regulatory agency and the IRS.

“Documents recently produced to the Committee demonstrate that FEC personnel communicated with IRS personnel about tax-exempt groups engaged in political activities,” Issa wrote.

The chairman of the House Oversight Committee cited emails between an FEC official and then-IRS Director of Exempt Organizations Lois Lerner, who earlier this year plead the fifth in testimony before Congress, in which the FEC official asked Lerner about tax-exempt applications pertaining to two conservative groups.

Issa said the communications between the two groups “raise the prospect of inappropriate coordination between the IRS and the FEC about tax-exempt entities.” He’s requested documentation for all communication between FEC and IRS employees from Jan. 1, 2008, to the present.

The Oversight chairman has fought to keep the investigation into the IRS’s alleged singling-out of Tea Party-affiliated groups in the public eye.

Last week, Issa subpoenaed IRS documents from the Treasury Department and on Tuesday, wrote an op-ed urging the White House and the IRS to be more cooperative in his investigations.

President Obama has denounced the investigation as an example of Republicans trumping up “phony scandals,” and the White House and Democrats have argued that Issa has produced no evidence to indicate the IRS’s processing of tax-exempt applications has been politically motivated.

The IRS defended itself in a statement, arguing that the agencies were coordinating to protect taxpayer information, but said it would “fully review” Issa’s request.

“The IRS emphasizes that it takes its obligation to protect confidential taxpayer information very seriously,” a spokesperson told The Hill.

“The email attached to the letter indicates that both Ms. Lerner and the FEC attorney recognized the IRS obligation to protect taxpayer information and that neither person wanted the IRS to provide the FEC with anything other than publicly available information," the spokesperson added. "Of course, the IRS intends to fully review and respond to the request from the chairmen.”

This story was updated on Aug. 8 at 11:54 a.m.