Nacional have apologised after some of their supporters were filmed making airplane gestures towards Chapecoense during a Copa Libertadores match on Wednesday.
A chartered plane carrying Chapecoense to the biggest match in the Brazilian football club's history crashed into a Colombian hillside and broke into pieces, killing 71 people and leaving six survivors in November 2016.
CONMEBOL, South America's governing body, confirmed it has launched an investigation because of "offensive behaviors that are an attack on human dignity."
In a statement Uruguayan club Nacional condemned the behaviour of their fans during the game at Chape's Arena Conda stadium, which finished 1-0 to the visitors.
"In the name of Club Nacional de Futbol, we send to [the CONMEBOL] president our deepest and most profound sentiment of embarrassment and strongly request for him to accept our apologies for the horrible and condemnable gestures made by two sections of our institution during yesterday's Copa Libertadores game," the statement read.
"Regrettably, many sick minds direct their irrationality at sporting events, and all clubs in competition, not just in our continent, but in others, are confronted with this scourge that, for as much effort that are made to combat it ... cannot put to an end such actions.
"The club is conducting the necessary investigations so that those responsible receive the most severe sanctions ... to determine their immediate expulsion, with consideration of other steps that may be adopted. Among them, communicating with the Uruguayan Football Association and security authorities so that those persons cannot attend sporting events."
Nacional also reminded CONMEBOL that this was an isolated episode and that in their Copa Libertadores home game against Chapecoense (in April 2017), the club's fans displayed acts of solidarity towards their Brazilian rivals -- they welcomed Chapecoense with a flag that had the words "Fuerza Chapecoense" and released white and green (Chapecoense colours) balloons before the encounter.
The club letter added: "For these reasons, because Nacional is a caring club, we vehemently repudiate the attitude of those that are unworthy of this rich institutional tradition."
Chapecoense finished the game with nine men after two players saw a straight red, and the visitors with 10. The return leg will be played next Wednesday in Montevideo.
ESPN FC's Adriana Garcia contributed to this report.