House Judiciary Committee Chairman John Conyers (D-Mich.) continued his tug-of-war Wednesday with Robert Luskin, attorney for former White House political chief Karl Rove, over whether Rove will testify before the committee about allegations of politicization at the Justice Department.

The Judiciary Committee is investigating accusations that Rove played a role in the controversial prosecution of former Alabama Gov. Don Siegelman (D) –– allegations that Rove flatly denies.

Luskin told Conyers in a letter last week that Rove cannot testify “on a variety of subjects related to the Department of Justice” because those matters are part of an ongoing legal dispute between Congress and the White House over the limits of executive privilege.

Nevertheless, Luskin offered to make Rove available for an interview by committee staff on the Siegelman case and said that as an alternative, “Mr. Rove is prepared to respond to written questions on the subject of the Siegelman prosecution.”

Conyers and other committee Democrats responded Wednesday that “we can see no justification for [Rove’s] refusal to speak on the record to the committee” and called Luskin’s latest offer “unacceptable.” Written questions would normally come after live testimony, the Democrats wrote, and there is no way to separate the Siegelman case from their broader concerns about the Justice Department.

The letter asks Luskin to “respond in writing no later than May 21 as to whether your client will make himself available to the committee for questioning.”