Hi John,
Issue of Form 16 is the right of the employee and a duty of the employer. First of all, you must have got form 16 for AY 2010-11. Form 16 for AY 2011-12 will be issued after 31 Mar 2011. Your employer can not prevent you from getting form 16. I don't know the legal way to get this but suggest you to keep safe the following documents with you as these will help you in getting your form 16 legally:
(a) Your Joining/offer letter.
(b) Your Salary Slips for all the months you were in employement.
(c) Your previos form 16 and other income tax declaration documents, your PF records.
(d) Any other document that can prove you were in employement with the company.
Hope the above will work.
Warm Regards,
Rahul Singhal