The following rights are being violated.
Right to Equality: Everyone is equal in the eyes of the law. No one can be denied admissions on grounds of birth. The person is practicing “untouchability” in an indirect way, and this is an offence in the eyes of law. His right to opportunity is also being violated.
Right to Freedom: Manoj has a right to apply for any job anywhere as long as he is citizen of country.
These two points should be pointed out in your letter to the District Collector