Termination notice without prior warnings about poor performance

Fristly, before assessing your situation, one needs to find out whether your brother falls within the category of 'workman' and whether the "daignositic centre" is an industry or not under the Industrial Disptues Act. What is the tenure of his service? What are the terms and conditions of his letter of appointment. The course of action would depend on these factual details before any legal action can be taken. This requires involvment of a lawyer who is specialized in this field. 

Since your brother cannot afford lawyer's fees ask him to contact the state legal aid committee which provides free legal aids to the needy.

Is your brother stopped at gate when he tried to enter into the office. 

If so after ascertaining the reasons he has to take legal action against the employer for terminating his services illegally without following the rules. 

If he cannot afford to bear the litigation expenses then he can avail free legal aid services from district legal services authority. 

The action is not legally sustainable. However, seeking legal remedy could be quite taxing.