The House Judiciary Committee has threatened to subpoena former White House adviser Karl Rove if he does not agree by May 12 to testify about former Alabama Governor Don Siegelman's corruption case.

In a letter to Rove's attorney Thursday, committee lawmakers called it "completely unacceptable" that the former Republican White House aide has so far declined the committee's request for sworn testimony even as he discusses the matter publicly through the media.

Since last year, Democrats on the committee have been investigating whether Rove and other Republicans influenced Siegelman's prosecution on bribery and other charges. Siegelman, a Democrat, was convicted in 2006 and sentenced to more than seven years in prison last year.