Yes, they can do that. However, I'll provide you certain legal suggestions, but for that i need to ask certain questions from you. For any further assistance, feel free to contact me on my e-mail "firstname.lastname@example.org"
Shubham Pabbi & Associates
Please reach me at 9794148274
1. Since your "friend" left job without notice, the company (employer) does not have any legal obligation to issue any salary slip or any other certificate.
2. Instead the company can declare him as absconder. He will find it very difficult to get another job.
3. The company can sue for damages for breach of terms as mentioned in the employment contract.
4. I suggest that your "friend" write a formal resignation letter to the company and try to solve the matter amicably with the management.
For consultation please write to me at email@example.com