Harris and the former president have both agreed to a debate, hosted by ABC News, on Sept. 10.
"Donald Trump is surrendering to his advisors who won't allow him to debate with a live microphone. If his own team doesn't have confidence in him, the American people definitely can’t," Harris said in a post on X.
"We are running for President of the United States. Let’s debate in a transparent way — with the microphones on the whole time."
Trump has said that he preferred to have his microphone kept on and that he did not like it muted during the last debate against then-contender President Joe Biden.
So-called "hot mics" can help or hurt political candidates, catching off-hand comments that sometimes were not meant for the public. Muted microphones also prevent the debaters from interrupting their opponent.
A representative for ABC did not immediately respond to a request for comment.
The debate would be the first time Harris and Trump face off since Biden dropped out of the presidential race following a poor performance at a CNN debate in June that raised doubts about his mental acuity.
Democratic vice presidential candidate Tim Walz and Republican vice presidential candidate JD Vance have agreed to an Oct. 1 debate on CBS News.
