While it is common for campaigns to quibble beforehand over debate mechanics, both Harris and Trump are under pressure to deliver a strong performance next month in Philadelphia.
The first debate during this campaign led to President Joe Biden's departure from the race.
Trump on Sunday night raised the possibility that he might not show up on ABC, posting on his Truth Social network that he had watched the network's Sunday show with a "so-called Panel of Trump Haters" and posited, "why would I do the Debate against Kamala Harris on that network?" and urging followers to "Stay tuned!!".
The current dispute centres on the muting of microphones when a candidate is not speaking, a condition both Biden and Trump accepted for their June debate hosted by CNN.
Both sides are accusing the other of gaming the system to protect their candidate.
Biden's campaign team made microphone muting a condition of its decision to accept any debates this year, and some aides now regret the decision, saying voters were shielded from hearing Trump's outbursts during the debate.
That move likely would not have helped the incumbent Democrat's disastrous performance.
The Harris campaign now wants microphones to be live all the time, according to Harris spokesman Brian Fallon, who issued a statement needling Trump.
"Trump's handlers prefer the muted microphone because they don't think their candidate can act presidential for 90 minutes on his own," Fallon said.
Harris "is ready to deal with Trump's constant lies and interruptions in real time. Trump should stop hiding behind the mute button".
Trump spokesman Jason Miller retorted that the Republican nominee had "accepted the ABC debate under the exact same terms as the CNN debate".
He alleged Harris' representatives sought "a seated debate, with notes and opening statements".
Miller then took a shot at Harris not sitting for an interview or holding a news conference since Biden ended his re-election bid and endorsed her, arguing her campaign now wants "to give her a cheat sheet for the debate".
The Harris campaign denied Miller's claim that she wanted notes or to be seated during the debate.
"I'd rather have it probably on," Trump said on Monday during a stop in the Washington DC area, when asked if he wanted microphones muted.
"I didn't like it the last time but it worked out fine," he added, in terms of the policy during his debate with Biden.
"We agreed to the same rules - same rules, same specifications," Trump noted, for his September 10 debate with Harris. "
And I think that's probably what it should be."
Asked how he was preparing for the debate, Trump responded, "I'm not ... I think my whole life I've been preparing for a debate".
Complicating the negotiations this year is that debates are being orchestrated on an ad hoc basis by host networks, as opposed to the bipartisan Commission on Presidential Debates through which debate rules were negotiated privately.
Microphones have been unmuted for both candidates for most of televised presidential debate history.
The debate commission announced that its October 2020 debate would have microphones muted when candidates were not recognised to speak after the first Biden-Trump contest descended into a shouting match.
The second 2020 debate with the microphone muting rules was widely celebrated for being more substantive than the earlier match-up.
