Lois Lerner, the top IRS official who is at the center of the controversy for the targeting of tea party and other conservative groups, will refuse to answer questions at a congressional hearing Wednesday and invoke her Fifth Amendment rights, ABC News has learned.

She is set to appear before the House Oversight Committee. Congressional aides said today that they received a notice from Lerner's lawyers that she would not answer their questions because it is now part of a criminal investigation.

"She has not committed any crime or made any misrepresentation, but under the circumstances she has no choice but to take this course," according to a letter that her lawyer, William Taylor, sent to Rep. Darrell Issa, chairman of the committee, which was first reported by the Los Angeles Times.

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Taylor asked that Lerner be granted a reprieve from appearing before the committee, saying it has "no purpose other than to embarrass or burden her." A congressional aide told ABC News that she is still expected to appear Wednesday.

Lerner is in charge of overseeing requests for tax-exempt status.

Her testimony is key, members of Congress believe, because she found out in June 2011 that terms like "tea party" and "patriots" were being used to flag tax-exempt requests. The practice stopped, according to an Inspector General's investigation, but she did not alert Congress.

A spokesman for the committee said Lerner remains under subpoena to testify.

"The committee has a constitutional obligation to conduct oversight," spokesman Ali Ahmad said. "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."

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