Holder orders IRS investigation

Attorney General Eric Holder has ordered the U.S. Justice Department to investigate the Internal Revenue Service's targeting of conservative groups for extra tax scrutiny.

Holder made the announcement during a news conference this afternoon, during which he called the bias against conservatives “outrageous and unacceptable.”

President Barack Obama used similar words when he denounced the IRS during a news conference Monday. He claimed he had no knowledge of what the IRS was doing until Friday.

An IRS official admitted on Friday the agency singled out Tea Party groups applying for tax-exempt status during the 2012 presidential election. She claimed the violation only occurred in one office and was initiated by low-level agents. But during the last four days, documents have emerged showing senior agency administrators knew about the practice as early as 2011.

Officials also now say the agency authorized extra scrutiny of many conservative groups, not just those associated with the Tea Party.

Republicans roundly denounced the agency on Sunday talk shows, and three Democratic senators joined the call for a formal investigation. The House will hold a hearing on the matter Friday.

The Associated Press contributed to this report.