Shane Ferguson celebrates scoring for Northern Ireland in the Milk Cup
A Northern Ireland fans group is appealing to Fifa to end what it calls the "football apartheid" in Ireland.
Fifa and the Court of Arbitration have ruled that NI-born players can opt for the Republic of Ireland.
The Amalgamation of NI Supporters' Clubs wants Fifa to have a re-think after Daniel Devine became the latest player to switch to the Republic.
It said the ruling gave the Republic an "unfair advantage" and accused the FAI of "poaching" players from N Ireland.
Fifa rules include a clause allowing players to change nationality once before they play a senior competitive match if they were born "on the territory of the relevant association".
The Good Friday Agreement of 1998 provided for Northern Ireland-born people to claim either British or Irish nationality.
Preston North End defender Devine has joined Darron Gibson, Shane Duffy, Marc Wilson, Daniel Kearns and Paul George in making the move to the Republic.
It is feared Newcastle United defender Shane Ferguson will be the next Northern Ireland youth player to switch to the Republic.
Amalgamation of NI Supporters' Clubs chairman Gary McAllister criticised the FAI in addressing the player drain to the Republic in an open letter in the Irish News.
"We believe this situation to be unique in world football, whereby one national association may select two jurisdictions worth of players," he said.
"Clearly this puts the Northern Ireland team at a disadvantage.
"For more than 50 years, the agreed and established practice of the two national football associations was always to select only those players with a territorial connection to either jurisdiction.
"It seems therefore that the FAI is using the Belfast (Good Friday) Agreement as an excuse for breaking this longstanding policy.
"This FAI policy is driving a sectarian wedge between the two communities in Northern Ireland in regard to football.
"We are hugely proud to support a team that includes members of both traditions in Northern Ireland, and want to continue to do so.
"We want an end to Football Apartheid in Ireland."
The open letter comes ahead of Tuesday night's Carling Nations Cup game between Northern Ireland and the Republic in Dublin.