Cambridge have told the supporters who booed players taking a knee at Tuesday's Sky Bet League Two clash with Colchester they "are not welcome" at the club and face a ban.
The return of a limited number of supporters at professional football matches was marred in the first weekend back by the conduct of some fans at the Football League games hosted by Millwall and Colchester.
The Football Association launched an investigation after players were booed for taking a knee in those December 5 fixtures, while there were more such incidents in League Two on Tuesday evening.
Exeter ejected a spectator from the ground after booing was heard when players took a knee in support of the Black Lives Matter movement ahead of their 2-1 loss to Harrogate at St James Park.
The Grecians vowed to "take the appropriate action" against the supporter on a night when multiple Cambridge fans booed the players' show of solidarity before the 2-1 win against Colchester at the Abbey Stadium.
In a statement released the following morning, the U's said: "It was hugely disappointing that, last night, a tiny minority should choose to boo when players took the knee before the start of the game, even if this was quickly drowned out by applause from the vast majority.
"We are not going to attempt to second-guess their motivation at what is clearly an act expressed to send an anti-racist message.
"We want to make clear that they are not welcome at Cambridge United. They do not share our values as a club.
"We will do what we can to try to identify them and when we do they will face a ban."
Cambridge manager Mark Bonner condemned the "unacceptable" incident immediately after the match, saying "a small number of fans let our club down".
Cambridge players Harvey Knibbs and Kyle Knoyle both posted on Twitter that they were "appalled and embarrassed by the section of fans who booed" the players taking a knee, saying "it's 2020 and the action is a symbol of solidarity".
The incident Cambridge left chief executive Ian Mather "incredibly frustrated" and "angry".
"The message to our fans is that behaviour is totally unacceptable," he told Sky Sports News. "We don't want to hear (it), we don't want anything like that here.
"We will decide on the appropriate sanctions. We will identify the right people and we will take action."
Asked how Cambridge can pinpoint the perpetrators and mete out punishment given no laws were broken, he added: "There are terms of entry into the Abbey Stadium as to any other stadium, so we can determine what behaviour is acceptable or not.
"That was not acceptable behaviour and we can decide what we do about it, and we will do that.
"Identifying them is actually quite easy. Somebody even sent me a direct message on Twitter last night explaining his views and others have been identified in other seats so finding them is actually not very hard."