If there is any Employer liability in case of Dual Employment?

Just wanted to check if there is any employer liability in the case of dual employment. After background verification, it was found that an employee's last working day was 21 Sep 2022, and the employee accepted the current company's offer to join on 6th Sep 2022. As employees have flexible working options and work from home, I understand this is unethical, and the employer can take disciplinary action; however, I need your expert guidance on employer liability, if any.

Employer's Liability: First or Second Employer?
Is the liability of the first employer, the second employer, or both? The first employer will have liability up to 21st September, while for the second, the liability would start from 6th September. The second employer has to take action when the fact of double employment is brought to its notice.