Rep. Darrell Issa (R-Calif.) on Wednesday ended a congressional hearing on President Obama’s political affairs office without testimony from scheduled witnesses, saying the discussion would not be “full and fair” without input from the White House, which defied a subpoena to have a senior adviser appear for questioning.

The abrupt end to the hearing came after tensions flared in an exchange of letters late Tuesday between the White House and Issa, chairman of the powerful House Oversight and Government Reform Committee. After briefing the panel’s staff Tuesday, a frustrated White House announced in a letter that political adviser David Simas would be a no-show for the hearing.

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

The congressional panel 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 long-standing 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 was “still under subpoena” and expected to attend the hearing.

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 they 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.

An appeals 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 George W. 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 “long-standing view that the president’s immediate advisers have absolute immunity from congressional compulsion to testify.”

Democrats argue that Issa has not justified the subpoena for Simas’s testimony.

“We do not simply haul in one of the president’s top advisers at will,” said Rep. Elijah E. Cummings (Md.), the panel’s top Democrat. “There must be a justification, some evidence that this official engaged in some type of inappropriate activity. That foundation simply does not exist.”

Cummings also noted that Issa indicated early on in his chairmanship that he would issue subpoenas only after seeking guidance from other panel members and putting the matter to a vote, something he did not do before demanding Simas’s testimony.

“If we cannot come to an agreement, a vote of the committee may very well be the most legitimate way to resolve a difference of opinion between us,” Issa said during a panel discussion after taking control of the committee in 2011.

Issa said the committee has a right and a responsibility to conduct oversight of the White House political office, saying that Obama administration officials have a record of violating the Hatch Act, which governs the political activities of federal employees. During his opening remarks Wednesday, he played a voice mail in which then-Labor Secretary Hilda L. Solis asked a subordinate to help with Obama’s reelection campaign.

“Just calling you off-the-record here,” Solis said in the recording. “Wanted to ask you if you could help us get folks organized to come to a fundraiser that we’re doing for the Organizing for America for Obama campaign. . . . There are a lot of folks that we know that are coming but wanted to ask you if you might help contribute or get other folks to help.”

Issa has complained that the White House opened its political affairs wing without consulting the Office of Special Counsel, which helps enforce the Hatch Act.

U.S. Special Counsel Carolyn Lerner submitted written testimony that said the political office appeared to be adhering to OSC guidance. She made clear, however, that her opinion is based on the office’s description of its work.

“To the extent that OPSO’s activities are limited to those described in the White House correspondence, OPSO appears to be operating in a manner that is consistent with Hatch Act restrictions,” Lerner wrote.

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

The political affairs office has sparked its fair share of controversy in past administrations.

Acting Special Counsel William Reukauf. 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. Additionally, 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.