The commission investigating the 11 September 2001 attacks on the US has been criticised for being "partisan".
The commission was set up to help prevent similar attacks in the future
Leading congressional Republicans Tom DeLay and Eric Cantor each sent letters to the commission chairman complaining about the tone of recent questioning.
House majority leader Mr DeLay said "partisan mudslinging" by members could undermine the panel's credibility.
The claims were rejected by the head of the commission, which has both Democrat and Republican members.
Mr DeLay said he was concerned by the style of questioning during recent hearings with National Security Adviser Condoleezza Rice and top officials from the FBI and CIA.
"Partisan mudslinging, circus-atmosphere pyrotechnics, and gotcha-style questioning do not get us closer to the truth," Mr DeLay wrote.
"The camera-driven tone of the hearings undermines the commission's credibility, distracts the American people from the gravity of the war on terror, and could send
dangerous messages to unfriendly eyes and ears around the world," he added.
Mr Cantor said the 10 panel members appeared more focused on apportioning individual blame rather than uncovering how the government functioned.
Its "myopic approach is too concentrated on pointing a finger at a single action or an individual rather than examining the long-term, systemic problems that led us to
9/11", he wrote.
'No conflict of interest'
But Thomas Kean, the Republican chairman of the commission, denied that politics was tempering its work.
"None of our votes have been cast on partisan lines," he responded. "All of us are striving to achieve a set of recommendations that can win the support of
He added: "We are committed as well to the integrity of our work. The commission has clear written guidelines on conflicts of interest."
The commission was established by the US Congress in late 2002 with the mandate to provide a "full and complete account" of the attacks of 11 September 2001 and recommendations as to how to prevent such attacks in the future.
It is due to release its final report in July.