Every employee is liable to get his minimum bonus if he's worked of atleast 30 days...... So yes, the principal employer is liable to pay the bonus.......
The question is not about the principal employer, but about the OCCUPIER of the employee's workplace, who occupies the premises, if in your case if it is principal employer is the occupier, then yes, he is liable.......... even the agent is liable if he is the occupier......
(I shall say the judgement is quite the old one, but no matter what it is, in any case if he proves to be an occupier then he will be made liable to pay the bonus. it doesn't at all matter whether he is the owner, or the employer or the agent, or the government itself... since it is the occupiers liability to pay the bonus unlike wages....... )