The White House is defying a subpoena from the House Oversight and Government Reform Committee, refusing to make a top political adviser to President Obama available for testimony Wednesday morning.

The clash is the latest skirmish over the powers of the executive branch and particularly the role of White House political advisers.

Tensions flared in a letter exchange late Tuesday between the White House and Rep. Darrell Issa (R-Calif.), chairman of the panel. After a day briefing congressional staff, a frustrated White House announced in a letter that political adviser David Simas would be a Capitol Hill no-show. Issa fired back that Simas was still expected to appear for the hearing, set for 10 a.m.

The House committee is questioning whether the White House Office of Political Strategy and Outreach, led by Simas, has used the department to raise campaign funds and support candidates.

White House counsel Neil Eggleston said in his letter to Issa that the subpoena for Simas’s testimony “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.” In his reply, Issa wrote that Simas is “still under subpoena” and expected to attend the hearing.

File: House Oversight and Government Reform Committee Chairman Rep. Darrell Issa, R-Calif. (AP Photo/Cliff Owen)

A White House legal team spent more than an hour on Tuesday briefing Issa’s staff on the political office’s activities, but Issa spokesman Frederick Hill said the administration’s lawyers did not answer questions about documents that the panel requested.

Administration officials rarely defy congressional subpoenas for testimony. When administrations have balked, however, it has sparked intense battles.

Issa contends that federal courts have rejected the notion that White House officials have absolute immunity from testifying before Congress.

A federal court upheld a 2007 subpoena by the Senate Judiciary Committee, which had demanded that then-White House Counsel Harriet Miers testify about the controversial firings of U.S. attorneys during the Bush administration. The court said Miers had to appear before the panel but didn’t have to discuss privileged information.

“Flouting a federal judge’s opinion about our system of checks and balances is yet another attack on our nation’s constitution by this president,” Issa said in a statement Wednesday.

The White House on Tuesday issued a legal opinion disagreeing with the Miers decision. Assistant Attorney General Karl Thompson said the Justice Department would stick to the executive branch’s “longstanding view that the president’s immediate advisers have absolute immunity from congressional compulsion to testify.”

Wednesday’s hearing is expected to go forward regardless of Simas’s absence. U.S. Special Counsel Carolyn Lerner and Scott Coffina, who served as a White House attorney during the George W. Bush administration, are expected to appear. Lerner’s agency, the Office of Special Counsel, enforces the Hatch Act, a statute that governs the political activities of federal employees.

FILE – David Simas, President Obama’s political director, left, and Rob Nabors, Deputy Chief of Staff (AP Photo/Charles Dharapak, File)

The White House political affairs office started under President Jimmy Carter. Obama closed the department as his reelection campaign was revving up in 2011. He reopened it in January.

In theory, the office is supposed to help presidents understand the nation’s political climate, as well as how their policies are affecting constituents. But the office has a history of sparking controversy.

OSC issued a report in 2011 that said the Bush political affairs office helped coordinate activities that violated the Hatch Act, including sending top appointees to election-battleground states such as Pennsylvania, Ohio and New Mexico.

In another high-profile case, President Bill Clinton and his political affairs staff orchestrated a campaign to raise funds and reward donors with White House perks, such as overnight stays in the Lincoln Bedroom, during his first term.

Issa once challenged OSC’s findings on the Bush political office, questioning the accuracy and motivation of the probe. In 2011, he launched an investigation of the OSC report, but little has come of the review except for a correction to an erroneous determination that one senator had not reimbursed the government for nonofficial expenses.

Democrats have criticized what they call the chairman’s overuse of subpoenas. Rep. Elijah Cummings (D-Md.), the panel’s ranking member, accused Issa of going on a subpoena binge since taking over as head of the panel in 2011, saying he has issued more subpoenas than the last three chairmen combined.

Cummings said in a statement Tuesday that Issa has offered “no evidence whatsoever to suggest that Mr. Simas or anyone on his staff did anything wrong.”