Can minimum service condition be enforced by an employer in the absence of any bond/surety

I am a regular/confirmed employee with a public sector unit (PSU) Govt. of India. I availed around 3.5 years leave (combination of earned leave - six months, commuted leave- three months and extraordinary leave without pay- about 2 years 9 months) for pursuing Ph.D. full time after due permission and leave by my employer. A clause' The officer has to serve for a minimum period of two years after completion of course' was included in my permission for studies, issued by competent authority. No contract/bond/sureties were got signed from me to that effect. I have served my organization for around 15 years before beginning this leave. After completing my PhD, I resumed duty with the organization and have completed around five months service before being offered appointment elsewhere, which I want to join. Please guide whether the two years service condition can fall in the way of acceptance of my resignation/one-month notice and if yes, what steps can I take to smoothen the process of my leaving my current organization. I need a proper relieving letter for my new assignment.