Founder threatening employees and not allowing a graceful exit

I won’t shy away from taking the name - Mr. Manas Sunita Pal, founder of Pedalstart(Gurgaon based) is threatening the employees against exit. Here are some of the ill-intent actions taken by him;

1. Threatening to provide bad feedback to next company/college if in case an employee leaves the company. He even sent out letters with poor feedback to college of some interns who left due to the toxic culture.
2. Asking employees to pay for the training and time spent in the company. According to him the employees are liable to pay to him as he has spent time with them training them.
3. Making employees work more than 18 hours everyday. Employees have a KRA where they have to take part in late night discussions at his flat and failing to do so would affect your promotions
4. Abusing the employees and using vulgar language against them

I know all this because I know a few people working at the company.

Can you folks let me know what could be the course of action for the employees. Can we do something to call out such toxic founders?