Dear Mostafa,
Immediate reply to the query would be yes, it is unlawful to terminate any worker on the spot. If the misconduct of the employee is serious, then the employer should order a domestic enquiry. If the misconduct is proved, then the worker may be terminated. Nevertheless, there are practical difficulties in implementation. If this legal process is followed in letter and spirit, then at the construction site, you need to have a dedicated room for conducting the enquiries. In the Indian context, it is beyond anyone's imagination.
The downside of the instant delivery of justice is that an innocent person may not get a chance to prove his point. It vitiates the work atmosphere. But then construction companies have to handle far larger issues and hardly have time to consider humans as a valuable asset of the business.
As a via media, you may give a show cause notice to the worker and ask for an explanation. If the explanation is not satisfactory, you may terminate the employee. By doing this, you will have at least some documentation at hand.
By the way, why was there a need to ask about the legality of the termination of construction workers? As such, they are in short supply, and even if you remove them, they can find jobs elsewhere. Thinking that such persons could raise an industrial dispute stretches one's imagination to an unreasonable level.
Last but not least, why bother about workers when your industry is known for on-the-spot removal of managers as well? Though I am making a sweeping statement, in the construction sector, bulldozers are used for construction activities as much as for bulldozing people. Therefore, be as it may and move on!
Thanks,
Dinesh Divekar