The White House is defying a congressional subpoena by keeping a top political aide to President Obama from testifying at a hearing Wednesday, setting up a potential new legal battle in this midterm election year.

The White House argued that Obama adviser David Simas is immune from the “extraordinary demand” of being required to testify before the House Oversight Committee as part of its investigation into the White House Office of Political Strategy and Outreach, which he directs.

White House counsel Neil Eggleston said in a letter Tuesday night to Darrell Issa (R-Calif.), the committee’s chairman, that the Simas subpoena “threatens longstanding interests of the executive branch in preserving the president’s independence and autonomy, as well as his ability to obtain candid advice and counsel to aid him in the discharge of his duties.”

The announcement came after White House lawyers spent an hour and 15 minutes Tuesday briefing the committee’s staff behind closed doors on the political office’s efforts to comply with federal law. But Issa said afterward that the committee still has questions he wants Simas to answer publicly.

Late Tuesday, Issa rejected the White House’s arguments, saying a previous court ruling had found that senior advisers to the president were not immune from congressional procedures.

“Assertions that this administration’s taxpayer-funded political efforts should be above congressional oversight are absurd,” Issa said in a statement.

Obama closed the White House Office of Political Affairs in 2011 but reinstated a slimmed-down version under the new name this year.