Employer Refusing To Disburse Retention Bonus

Hello,
I need advice on pursuing my case for retention bonus with my previous employer on legal terms.
My annual compensation had a component for retention bonus which is paid on successful completion of one year. I resigned after 9 months of employment and served 3 months of notice period and thus completed exactly 1 year and 7 days in the company.
Now, during Full & Final settlement, the employer is refusing to pay the retention bonus component of Rs. XXX.
I requested multiple times but the employer is not ready to budge. So, I need legal advice to pursue the matter. Following are more details:
Date of joining: 20th Jan 2015
Date of resignation: 6th Nov 2015
Date of leaving: 29th Jan 2016
Terms mentioned in offer letter / appointment letter:
"Your total annual remuneration on Cost to Company basis will be Rs. XXX which includes Rs. XXX as Retention Bonus paid at successful completion of one year".

Please send us your role in the company and tell us whether you have been working as Manager or supervisory capacity with at least one person reporting to you. Please do not put " XXXX" against your designation also.
Madhu.T.K

Many thanks Mr. Madhu for you reply.
Please find below required details:
Designation: Project Manager
# of reportees: More than 10
CTC per Anum: Rs. 1500000
Retention Bonus: Rs. 100000

In this scenario the management can withhold or forfeit the retention bonus because you have not completed the required period of service "successfully". This is a word which will always protect the employer. If the employer says that he is not happy with the performance of the manager and hence whatever salary paid to him should only be regarded as the amount payable and nothing additional shall be paid when his service itself is not required, you cannot challenge it.
However, in the case of an employee who is neither designated as manager nor given any supervisory function, the things would be difficult because the labour law will protect him if he had a different interpretation of total salary or the amount which will be released after one year of service.
Madhu.T.K