Concerns About Employment Conditions
Though I concur with M/S KK!HR and Nathrao on their explanatory note about the unconventional condition imposed by the particular management for the purpose of retaining talented employees in the organization, I would emphasize that such a condition smacks of an indirect bonded labor system. This condition also implies that no resignation would be accepted within the stipulated period.
Suppose an employee finds a better opportunity within a year or two and submits their resignation. Most probably, it would not be accepted but only rejected to avoid documentation of a formal relief. Naturally, the employee would be tempted to walk out without formal relieving orders as well as an experience certificate, deeming the explicit condition in the offer letter already issued as proof of their tenure in the company.
Then, the management can play the game of employment abscondment and torture the employee or spoil the background verification with a wanton claim of the continuation of their services on record. Therefore, I would suggest that if the questioner is optimistic about their employability and shrewd enough, they can negotiate with the management to substitute the condition with a sufficiently long notice period, if any, as they deem reasonable.