Dear Manmadha,
To my knowledge, not only the Factories Act, 1948, but also no other laws providing for leave benefits to employees require furnishing a proper reason for leave applied for. Leave is an employment benefit conferred on the employees primarily for the purpose of rejuvenating the body and spirit of the employees to regain vigor in the usual process of continuous work. It also aims to strike a work-life balance and enable employees to fulfill their social obligations like other members of society.
Furthermore, upon analyzing the different types of leave and the associated restrictions on sanction, in my considered opinion, there is no need to require employees to provide a proper reason when applying for leave. The phrase "proper reason" is subjective and cannot be objectively defined to satisfy both the employer and the employee.