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

In a letter to Rove's attorney, committee Democrats called it "completely unacceptable" that the Republican political strategist has rejected the panel's request for sworn testimony even as he discusses the matter publicly through the media.

"We can see no justification for his refusal to speak on the record to the committee," the letter states. "We urge you and your client to reconsider ... or we will have no choice but to consider the use of compulsory process."

Committee Democrats are investigating whether Rove and Republican appointees at the Justice Department influenced Siegelman's prosecution to kill his chances for re-election. It is part of a broader inquiry into whether U.S. attorneys were fired for not aggressively pursuing cases against Democrats.

Siegelman, a Democrat who served one term as governor after being elected in 1998, was convicted in 2006 on bribery and other charges and sentenced to more than seven years in prison. He was recently released on bond pending appeal.

Last year, Alabama attorney and one-time Republican campaign volunteer Jill Simpson, told the committee under oath that she heard conversations among GOP operatives in 2002 suggesting that Rove was pushing the Justice Department to pursue a conviction against Siegelman. She also has said Rove asked her in 2001 to find evidence that Siegelman was cheating on his wife.

Rove, who frequently worked in Alabama politics before orchestrating President Bush's White House campaigns, has denied having anything to do with the case. In a recent magazine article, he called Simpson a "complete lunatic" and said he had never heard of her.

The career prosecutors who handled Siegelman's case also have denied any political influence.

Thursday's threat marks the latest development in a lengthy standoff between President Bush and Congress over testimony from current and former White House staffers.

The committee has issued or threatened subpoenas to more than half a dozen administration officials and is suing White House Chief of Staff Josh Bolten and former presidential counsel Harriet Miers for refusing to comply with subpoenas on the U.S. attorney firings.

The White House has generally maintained that their testimony is off-limits from congressional oversight under executive privilege.

Rove's attorney, Robert Luskin, maintains that Rove must defer to that position. But as the White House has offered on other matters, Luskin wrote the committee this week that Rove would discuss the Siegelman case on the condition that his comments not be under oath and not be transcribed.

Judiciary Committee Chairman John Conyers, D-Mich., and several other lawmakers rejected the offer, saying such an interview "will not permit us to obtain a straightforward and clear record."