Which form to submit W-4 or Form 8233 as a NRA on F1-OPT?

[user17553787901]

I am an NRA on F1-OPT and started working as full time employee. I am eligible for tax treaty benefits under Article 21(2); however my new company has not considered it. They have asked me to submit Form W-4, which has NRA marked at step 4(c).

My question is :

1. Do I need to submit Form 8233 instead of W-4? My employer says form 8233 is only for independent contractors and not applicable to me since I am full-time employee.

2. Is there a different correct way to have the employer correctly consider tax treaty benefits?

Which form to submit W-4 or Form 8233 as a NRA on F1-OPT?