The plans for the square in Dublin 6 to include an all-weather pitch with floodlights has divided residents.
Campaign groups with professional PR advisers have been set up by opponents and supporters of the project.
Objectors have dubbed the plans as the school’s “private Aviva”.
The Protect Kenilworth Square group, which includes residents from the Victorian red-brick square, has raised more than €60,000 to fund a High Court challenge to Dublin City Council’s approval of the first phase that allows St Mary’s College in Rathmines to replace a grass rugby pitch with an all-weather synthetic pitch.
St Mary’s, which has owned the park since 1947, says the redevelopment will allow it to rent the new all-weather pitch to local soccer and GAA teams amid a shortage of suitable training grounds in south Dublin. The park is not open to residents.
Bacik said the square “must be protected from the Spiritans/St Mary’s College Rathmines’ wholly inappropriate development plans”
A Kenilworth for Kids group, set up by parents of St Mary’s pupils, is promoting the redevelopment. Its petition has been signed 2,050 times.
The Protect Kenilworth Square group, whose posters opposing the redevelopment adorn most of the houses around the square, has 2,900 signatures.
Ms Bacik was the first prominent local politician to take sides publicly when she posted a video on her social media accounts. She said the square “must be protected from the Spiritans/St Mary’s College Rathmines’ wholly inappropriate development plans”.
She wrote to the council in August raising concerns.
Labour has proposed designating the square as an Architectural Conservation Area and asked if the tree preservations orders could be made.
Ms Bacik’s video sparked a number of negative comments from supporters of the school.
The Labour leader deleted it from her social media in recent weeks. saying she had done so because of the legal action.
“As a parent, I have had many experiences of matches and training being cancelled due to waterlogged pitches or lack of access to pitches in our area,” she said.
Ms Bacik said she has worked to get greater access to playing fields across Dublin 6.
She had met with the school and residents to seek a “compromise” so local clubs and children could access improved playing facilities in the park, “while ensuring that concerns about environmental impacts could be meaningfully addressed”.
We were disappointed to see certain political figures initially opposing the much-needed upgrades at Kenilworth
Mary Daly, a spokeswoman for Kenilworth For The Kids, said: “We were disappointed to see certain political figures initially opposing the much-needed upgrades at Kenilworth.
“Like the residents of the square who over the years have modernised their homes and gardens, St Mary’s is modernising its sports grounds to meet 21st-century needs while carefully respecting the area’s heritage.
“The school has pledged to share its improved pitches with local clubs and teams, just as it has shared its front pitch in recent years which has been a great success. This generosity deserves recognition and should inspire others.”
Martin Joyce, the Protect Kenilworth Square spokesman, said allegations of misinformation were an attempt to divide the community.
“We have almost 3,000 petitions signed in the wider community and 93% written support from local residents,” he added.
“All our information is accurate and honestly presented in response to the plans and information published by St Mary’s College and/or its developers.
“For the record, Protect Kenilworth Square supporters are opposed to the published plans to excavate the park and put in a plastic pitch, a 1.2m surrounding fence and six 18m-high floodlights, remove heritage trees, install a car park and build a very large new pavilion.
“It is a wholly inappropriate plan.”
Candidates for the major parties standing in the Dublin Bay South constituency were asked if they support the project.
Sinn Féin TD Chris Andrews and Nick Delehanty, an Independent, said they supported the plans. Emma Blain, a Fine Gael candidate, said she would not comment because of the legal case.