Hi,

So, I am an F1-OPT student, working in Boston and originally from India and wanted to know if there is any formal way of communicating to the employer about the FICA exemption (an official form?) in my case (I am in US since August 12, 2010).

I have completed the form w-4 where I mentioned my non-immigration status and showed my employer the relevant section in the IRS website, which has the guideline for FICA tax exemption, in my case. Would that be enough?

I was then told that if the form w-4 has been filled correctly, the FICA would be exempted? I did not get that so just wanted to know - what specific part of the form w-4 is relevant to the FICA exemption?

You would write on the form "non-resident alien" on the dotted line, line 6.
Showing your employer the IRS code should be enough. Just make sure on your paycheck, that they are not withholding FICA.
When you change status, you need to inform your employer immediately.

Special Instructions for Form W-4 For Nonresident Alien Employees

A nonresident alien subject to wage withholding must give the employer a completed Form W-4 to enable the employer to figure how much income tax to withhold. In completing the form, nonresident aliens should use the following instructions instead of the instructions on Form W-4.

For Forms W-4 completed after December 31, 2005:

Check only "Single" marital status on line 3 (regardless of actual marital status).
Claim only one withholding allowance on line 5, unless you are a resident of Canada, Mexico, South Korea, a U.S. national, or a student or business apprentice from India.
Do not claim “Exempt” withholding status on line 7.
Write “Nonresident Alien” or “NRA” above the dotted line on line 6 of Form W-4.

http://www.irs.gov/businesses/small/international/article/0, id=106274,00.html

Download IRS Pub 519 from www.irs.gov and print off pages 53-58. That contains the provisions that explains that F-1 visaholders are exemption from FICA (Social Security and Medicare) taxes.

That should be sufficient to convince your employer to STOP withholding the FICA taxes and refund those taxes already withheld.