A top IRS official scheduled to testify Wednesday before the House Oversight committee has notified Congress that she will invoke the Fifth Amendment and refuse to answer questions.

Lois Lerner, head of the IRS unit which handled tax-exempt organizations, won't answer questions about what she knows about the improper screening of conservative groups or about why she repeatedly failed to tell Congress that such targeting was going on, according to a letter from her lawyer, William W. Taylor 3rd.

The news of Lerner's intention to invoke the Fifth Amendment was first reported Tuesday by the L.A. Times.

Some members of Congress have called for Lerner to be relieved of her responsibilities. Rep. Darrell Issa (R-CA) alleged that she gave false and misleading testimony to Congress.

Her lawyer wrote, "She has not committed any crime or made any misrepresentation, but under the circumstances she has no choice but to take this course."

A spokesman for the House committee said: "The Committee has been contacted by Ms. Lerner's lawyer who stated that his client intended to invoke her Fifth Amendment right and refuse to answer questions. Ms. Lerner remains under subpoena from Chairman Issa to appear at tomorrow's hearing -- the Committee has a Constitutional obligation to conduct oversight. Chairman Issa remains hopeful that she will ultimately decide to testify tomorrow about her knowledge of outrageous IRS targeting of Americans for their political beliefs."

An FBI criminal investigation has been launched into whether any of the IRS actions were illegal and potentially into whether senior officials lied to Congress. Given that, testifying under oath carries added legal risk.