Disgruntled parents posted the letter on social media which was received with outrage by many, with some accusing the school of being intolerant of the Muslim faith.
The letter, dated May 27, suggested Muslim pupils had to write exams on the morning of Eid.
SA Democratic Teachers Union (Sadtu) provincial secretary Jonavon Rustin said: “The school did not observe religious tolerance.
"We are saying the school needs to reschedule exams because of Eid. The school needs to have an inclusive policy that caters for all faiths.