Dear Mostafa,
Immediate reply to query would be yes, it is unlawful to terminate any worker on the spot. If the misconduct of the employee is serious then employer should order domestic enquiry. If the misconduct is proved, then 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 Indian context, it is beyond anyone's imagination.
The downside of the instant delivery of justice is that innocent person may not get chance to prove his point. It vitiates the work atmosphere. But then construction companies have to handle far larger issues and hardly they have time to think human as valuable asset of the business.
As a via media, you may give show cause notice to the worker and ask for explanation. If the explanation is not satisfactory, you may terminate the employee. If you do this, you will have at least some documentation at hand.
By the way, why the need was felt to ask the legality of the termination of construction worker? As such they are short in number and even if you remove them, they get the job somewhere else. Thinking that such person(s) could raise industrial dispute is stretching one's imagination to the unreasonable level.
Last but not the least, why bother about workers when your industry is known for on-spot removal of the managers also? Though I am making bit sweeping statement, but then in the construction sector, bulldozers are used for construction activity as much for bulldozing people. Therefore, be as it may and move on!
Thanks,
Dinesh Divekar