Swim Ireland has confirmed that Ireland's 4x100 Medley Relay team have had their Olympics invitation rescinded by swimming's governing body FINA after it was "issued in error" on Saturday afternoon.
In their statement, Swim Ireland announced their attention to challenge the decision.
On Saturday, it was reported that two Irish men's relay teams had qualified for the Olympics.
The 4x200m Freestyle team of Jack McMillan, Jordan Sloan, Finn McGeever and Gerry Quinn and the 4x100m Medley team of McMillan, Shane Ryan, Darragh Greene and Brendan Hyland had both qualified for the Tokyo games as wildcard picks.
It was to be the first time since 1972 that Ireland would send two swimming relay teams to an OIympic Games.
However, FINA contacted Swim Ireland on Sunday to say that the invitation to the 4x100 Medley team had been rescinded as it had been issued in error.
The invitation to the 4x200 Freestyle team is unaffected.
Swim Ireland said they were "extremely disappointed" at the development and noted the impact on the affected athletes. They added that they were exploring their options.
Swim Ireland statement:
"Swim Ireland can confirm that we received correspondence on Sunday, 6 June from FINA rescinding their invitation for Ireland to compete in the Men's 4x100m Medley Relay at the Tokyo Olympic Games.
"Having received and accepted FINA’s invitation to compete on Saturday, 5 June, we are extremely disappointed that FINA have told us that the invitation was issued in error, particularly given the impact on the affected athletes. Our intention is to challenge the decision and we are currently exploring all options in this regard.
"The invitation for Ireland to compete in the Men’s 4x200m Freestyle relay is unaffected. The Tokyo Olympic Games will be the first time since 1972 that Ireland has competed in a swimming relay and the first time ever that an Irish male relay team will compete."