I submitted several doctors notes substantiating my disability for an accommodation request. My supervisor has been accommodating me for 2 years. Suddenly I'm told I need to be examined by their MD to see if I really have a disability. Since I have already provided substantial medical documentation of my medical condition and how it is not temporary, am I required to see their MD?

Are you asking about being examined by a company/employer Physician OR a Physician with an insurance company which writes the employer's coverage?

Yes, they can require that you see a physician of their choosing.

Being examined by a company/employer Physician. I have submitted doctors notes from 2 MDs(my primary & my specialist) with the medical info mgmt requested.

Doesn't matter, they can require that you see a physician of their choosing, but they have to pay for it.

They have the right to see if this is a true disability, many people have doctors who will sign almost anything ( sorry but it is true) Also depending on the cost of this and the type of disabilty they may want to know their legal risk with this.

But yes, they can ask for you to see their doctor,
If they wish to deny it because of his opinion, then you will hire an attorney and have to go to court over the doctors opinion.

But if this is a true disability, then it should be easy to prove to the other doctor

Not only is this their right, but there is more and more concern with company liability insurance, and they need to know just what might happen if something in the buildings and grounds might affect those with less than the usual ability to use them. This might have even been a new requirement of their insurer.

If they deny you accommodations for your disability after the exam, then come back and ask for more advice. You haven't said what they are, so we would need to know then, as well as if you were hired with the disability known to them, or it happened after.