House investigators are interviewing two front-line Internal Revenue Service employees from the Cincinnati tax exempt office this week in Washington, and plan to interview two others next week, two congressional sources familiar with the investigation tell CNN.

House investigators are hoping these IRS employees will shed light on exactly why tea party and other conservative groups were inappropriately targeted for excess scrutiny when applying for tax exempt status.

The sources would not yet disclose the names of the employees, but CNN has previously reported that House Oversight Chairman Darrell Issa requested transcribed interviews with four IRS employees from the Cincinnati tax exempt office: John Shafer, Gary Muthert, Elizabeth Hofacre and Joseph Herr.