Cummings never told committee Republicans about his contacts with the IRS concerning the group True the Vote. In fact, he has denied any such contact.
In a letter to Cummings on Wednesday, Oversight Committee Chair Darrell Issa (R-Calif.) and other committee Republicans said Cummings' inquiries about True the Vote may have prompted additional IRS scrutiny of the group.
The letter also notes that Cummings' email communications with the IRS "raise disturbing concerns about your possible motivations for opposing this investigation and your unwillingness to lend your support to efforts to obtain the testimony of former IRS Exempt Organizations Director Lois G. Lerner."
Committee Republicans also question whether the IRS had "improperly shared protected taxpayer information" with Cummings' staff.
The letter details Cummings' staff's contacts with Catherine Engelbrecht, president and founder of True the Vote, who testified that she received three letters from Cummings' office, demanding the same information that the IRS wanted from her.
Engelbrecht's attorney, Cleta Mitchell, raised the possibility that Cummings' staff had coordinated with the IRS in targeting True the Vote.
The letter to Cummings notes that Lois Lerner appeared "personally interested in fulfilling your request for information about True the Vote," and it included in its letter transcripts of emails from Lerner.
On Thursday, the Oversight Committee is expected to hold Lois Lerner in contempt of Congress for refusing to answer questions about the IRS targeting of groups that applied for tax-exempt status. Lerner headed the office that handled those requests.
"As the committee continues to investigate the IRS' wrongdoing and to gather all relevant testimonial and documentary evidence, the American people deserve to know the full truth," Committee Republicans wrote to Cummings.
"They deserve to know why the Ranking Member and Minority Staff of the House Committee on Oversight and Government Reform surreptitiously contacted the IRS about an individual organization without informing the Majority Staff and even failed to disclose the contact after it became an issue during a subcommittee proceeding."