Thank you for your questions.
1. What is the best line of action to take to get these unpaid bonuses?: We suggest that you follow the same process as you would for unpaid salary in order to make a claim for the unpaid bonus. You can find out the process here – http://lawpadi.com/latenon-payment-salary/
2. What is the Nigerian legal position on this type of bonus?: There is no law that prevents this. It is a perfectly legal arrangement between an employer and an employee.
3. Will it be wise to take legal action against a present employer on this issue?: This is entirely up to you, however a more practical solution would be to try to negotiate with the management of the company for the bonuses.
We hope you have found this information helpful. Please note that this information is provided for general informational purposes only and is not intended to be legal advice. No lawyer-client relationship is formed nor should any such relationship be implied. It is not intended to substitute for the advice of a qualified lawyer. If you require legal advice, please consult with a qualified lawyer.