The Department of Education spent more than €104m on the salaries of teachers in private schools last year.
It is an increase of over €7m on the previous year.
Just over 26,000 boys and girls attended fee-paying schools during the 2020-21 academic year.
According to Freedom of Information figures, the State spent €104m on their teachers' salaries - up from €97m on the previous year.
The Social Democrats' education spokesman, Gary Gannon, says the system should be overhauled.
"Parents of wealthier students use private schools as a way of locking in their privilege.
"And the fact that each year, now, the State aids that to the tune of 104m this year, raises questions about 'Is the State aiding wealthier people to lock in their privilege'.
"Why does the parent of little Johnny who can afford to go to a private school also get the benefit of a massive State subsidy of 104m?
"All the while locking in their privilege for their son over another from a less privileged family".
Teachers in St Andrew's College in Dublin got over €4.3m - which is the highest in the country.
The second highest was Blackrock College in Dublin, at just under €4m.
And teachers in Wesley College, also in the capital, were paid nearly €4m by the department.
All three schools had around 1,000 students each during the year.