Can Employers Really Stop You from Working Elsewhere? Seeking Advice on My Sister's Situation

I have a doubt. Please give your guidance. Currently, my sister is working in a share market job in a local place. Her manager has told her to give one month of notice. He recalled a past incident that happened in the company. One of their employees left her job without giving a resignation letter due to some personal reasons. That employee received a letter from the Delhi Head Office instructing her not to work anywhere. My sister's manager mentioned this. The company did not provide a confirmation letter, appointment order, payslip, or any agreement.

Can Employers Prevent Employees from Working Elsewhere?

My question is, can they prevent an employee from working anywhere else? Is it possible for employers to stop an employee from working in other companies? Kindly guide me.

Unethical Practices in Employment

Many employers adopt unethical methods, exploiting the helplessness of job seekers. This trend is also witnessed in IT/ITES, where mostly engineers and highly educated individuals are employed. Unless someone exposes the wrongdoings of these employers, solutions are merely an illusion.

Challenges in Employment Restrictions

Preventing a person from getting employed elsewhere may be possible in instances when reference/background checks are conducted by prospective employers, leading to the passing on of unpleasant or unsatisfactory reports. Additionally, there are bonds and other terms and conditions of employment that prohibit exiting employees from seeking employment with competitors or companies in the same field. Generally, such restrictions will not withstand the test of law in courts. For those not facing such preconditions, things may be more comfortable.