More than 20 schools will suffer from increased noise levels because of proposed changes at George Best Belfast City Airport, a residents' campaign group has claimed.
The airport has put forward noise control measures but lobby group Belfast City Airport Watch said 21 schools in Belfast and Holywood, Co Down, would be affected by the possible new limits.
A spokeswoman for the airport said they had never received complaints from local schools.
The proposal by George Best Belfast City Airport would replace an existing passenger cap with one controlling noise.
Teaching union the Association of Teachers and Lecturers (ATL) expressed concern.
Northern Ireland director Mark Langhammer said: "We are very concerned at the potential impact of these proposals, given the evidence which exists on the detrimental effect on children's education of aircraft noise.
"We would not want to see any drive for airport expansion take place at the expense of children's education.
"Many of the schools identified by the airport are in areas which suffer from social deprivation.
"Their pupils are already at an educational disadvantage due to their backgrounds - they don't need the further handicap of excessive aircraft noise."
Airport officials are seeking to modify a planning agreement between the city hub and the Department of Environment ruling that operators using the airport may not sell more than two million scheduled flight seats in any 12 month period.
Instead, the airport is proposing to remove the "seats for sale" restriction and put in its place noise control measures.
A total of 21 schools are affected by proposed increases in permissible noise levels, according to the residents' group, including two top grammar schools, a private prep school, 11 primary schools, an infant's school and four nurseries.
Katy Best, director of business development at George Best Belfast City Airport, said: "We are extremely concerned that once again Belfast City Airport Watch is attempting to use children to try and convey a point.
"The airport has never received a complaint of any nature from any schools nor education boards concerning noise.
"We have a very close working relationship with schools and teachers in the area and many of our staff have children enrolled in local schools."
She said the airport had volunteered a strict noise contour control cap and other noise control measures to protect all residents from any future development at the airport.
"While we acknowledge that noise is associated with all airports, Belfast City has one of the lowest noise complaint rates of any UK airport, with 41 recorded in 2011," she added.
"Any future development will be within accepted government guidelines."
She said the seats for sale limit related to a terminal building long since demolished, adding it was an irrelevant measure as the airport was prohibited from flying more than 48,000 flights annually.