The Department of Education spent over €97m on the salaries of teachers in private schools last year.
The new figures have been released to Newstalk under the Freedom of Information Act.
The department pays the salaries of teachers in 52 fee-paying schools across the State.
In the 2019/2020 school year, they were attended by nearly 11,000 girls and almost 15,000 boys.
The cost to the State of the teachers' salaries was just over €97m - nearly €1.7m more than the previous year.
The highest amount last year was paid to teachers in St Andrew's College in Dublin, at over €3.9m.
Arthur Godsil, a former headmaster of the school, says the State should continue to fund the salaries of teachers in fee-paying schools.
"The economic argument is strongly in favour of retaining the current system.
"If all the schools were to go into the free scheme, the teachers would still have to be paid, the children would still have to taught".
But Sinn Féin's education spokesman, Donnchadh Ó Laoghaire, says the State's financial support of these schools should be phased out.
"If people want to educate their children privately that's entirely their prerogative.
"It's entirely the prerogative of the schools to organise that - but we don't agree with the families of those who have children in schools with high disadvantage that are underfunded should be subsiding with their taxes".
Apart from St Andrew's College, the salaries of teachers in five other schools also cost the State more than €3m last year.