Aides for the House Ways and Means, Oversight and Government Reform committees told Politico members hope the four employees from the agency's Cincinnati office will shed light on the roots of the scandal that has engulfed the Internal Revenue Service.
An Oversight Committee aide declined to name those who would be interviewed.
The Cincinnati office is where the agency processes applications for tax-exempt status.
CNN first reported the broadened investigations Thursday.
Republicans on both committees have questioned whether politics was the motivator for decisions by Cincinnati employees to flag groups for deeper review if their tax documents had the words "Tea Party" or "patriot." The IRS said the review was not politically motivated.