Company force to singn offer letter with condition

Show your appointment letter to a local prudent lawyer for proper appreciationn of facts and professional advise.

If the company has given cash bonus in the beginning or at any time later for the purpose of your accepting or continuing in the employment and you had accepted it, you are bound by the terms of the contract. 

Under Indian law, salary is governed mainly by the Payment of Wages Act, 1936 and general contract law principles under the Indian Contract Act, 1872. 

An employer cannot simply stop paying salary for work done.

Companies generally adjust bonuses or recoverable dues against final settlement (F&F), deduct recoverable amounts only in the final settlement, not by stopping salary entirely.

If the contract  states that a minimum service period (e.g., 3 years), and repayment if leaving early, then recovery of the joining bonus is usually enforceable. 

But the company cannot impose arbitrary penalties beyond the contract.

Conditional bonus is enforceable, i.e., you do not have to return if you serve the full period but if you leave early then you may have to return proportionately.

Please note that the Companies generally must issue employment records, and refusing documents to force payment may be considered unfair labour practice in disputes.

The company may delay full-and-final settlement, delay relieving letter until dues are cleared, but they cannot blacklist you or stop you from joining another company.

Under the proviksions of section 27 of the Indian Contract Act, 1872 Section 27, which says agreements restraining trade are void, i.e., post-employment non-compete clauses are usually NOT enforceable.

You may Negotiate before resigning because many companies reduce recovery amount if you join a non-competitor or if you complete partial notice of if the new employer buys out the bonus. This is the most common outcome