The NSW Education Standards Authority is investigating Sydney schools linked to the conservative Catholic group Opus Dei.
Premier Dominic Perrottet confirmed NESA had been asked to investigate "broad concerns" about the curriculum at the schools, to be broadcast by the ABC's Four Corners program on Monday.
Mr Perrottet is an alumni of one of the schools, Redfield College, where he was school captain in 2000.
"When complaints are made in relation to any government service we refer those to the relevant authorities," he told reporters.
"Broad complaints were made in an email to my office and we did what we would normally do and referred them to the authority," he said.
The schools, including Tangara School for Girls, Wollemi College and Montgrove College are independent and affiliated with Opus Dei and are not part of the Catholic education system.
Education Minister Sarah Mitchell said "broad allegations" had been made about "teaching to the curriculum".
Mr Perrottet says any allegations of impropriety would be investigated and the curriculum always needed to be followed but added "it's not a crime to be Catholic".
"We live in the most tolerant country almost anywhere in the world and we respect people who practice faith, who don't practice faith," he said.
"I am a strong believer in parental choice when it comes to education."
