Employee Not Ready To Serve The Notice Period After Sending Resignation Mail.

Dear Seniors,
One of our employee is joined recently and few days back he resigned station that he is having some family issue. We accepted his resignation and asked him to serve the notice period. He agreed to serve the notice period but suddenly today he sent a mail station that he is not ready to serve the notice period. We tried reaching him but he is not responding the call. Management is asking to take a legal action is it possible to take action immediately?
Kindly suggest what best can be done in this scenario.
Regards,
Sharad Kumar.

You shall send me ref letter to his resignation .Secondly this shall be send through registered post and then show caused notice for this.
Kind Regards,