Sen. Roger Marshall, R-Kan., is demanding ABC News release any communication it had with Vice President Kamala Harris' campaign before the presidential debate earlier this month, The Hill reported.
"On debate night, it became abundantly clear that ABC News and its respective moderators had a biased agenda," Marshall wrote in a letter to ABC News President Almin Karamehmedovic and Harris' campaign manager Julie Chávez Rodriguez.
"Over 67 million Americans watched as a policy exchange between two presidential candidates quickly turned into a three-on-one debate against the Republican nominee," Donald Trump, he added.
"The American people deserve transparency and accountability from the mainstream media and a full accounting of whether ABC News coordinated with the Harris campaign to skew the debate's questions and fact-checking in favor of the vice president."
Marshall last week vowed to investigate claims ABC News debate moderators were "biased" against Trump and coordinated with Harris ahead of the Sept. 10 debate.
The network has denied the claim.