Unless I see the letter and know more information about your father there is no way to answer your question. I do suggest that he consult with an experienced immigration attorney before he goes to the interview. The attorney may have some suggestions as to what he needs to do and why they want to speak with him. Depending on the situation it may also be advisable that the attorney attend the interview with him.
You told us that he is the family provider .... but you didn't tell us what his immigration status is.
This form is used to save the government money ... instead of going to his house ... they're having him come in to be arrested.
It is normally issued when people are already 'in the system'. Did he appear before an immigration judge years ago?
HIRE A LAWYER ... DO NOT LET HIM GO IN ALONE.
DO NOT IGNORE THE LETTER.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
They want to know whether he is legal here.
NYC EXPERIENCED IMMIGRATION ATTORNEYS www.myattorneyusa.com; email: firstname.lastname@example.org; Phone: (866) 456-8654; Fax: 212-964-0440; Cell: 212-202-0325. The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter.