Im a server, and I threw my back out yesterday. The doctor said to rest today and not do any lifting, but apon calling work this morning I was told I was going to be written up for excessive absence (I was ill earlier this year) if I did not come in and work my shift. Is this legal?

Unless the absence is FMLA-related, a doctor's note need not be given any weight by the employer.

Not the way I would handle it, but very likely not illegal either.

I believe I am covered through FMLA, I have worked for the company for 3 years, and average out at 1400 hours a year, and there are over 50 employees within 75 miles.

But is the injury a serious health condition as defined by the statute?

I would think so? It does prevent me from doing my job, as the doctors note states. I mean, they gave me some pretty heavy duty pain killers and muscle relaxers

Here is the legal definition of a serious health condition.

http://www.dol.gov/elaws/esa/fmla/shc.asp

So if im only required to have 2 days off im not covered?

That's right.

That's simplifying it, but pretty much, yes. Also a factor is that you are not receiving continuing medical treatment (other than the meds).

ok, so what if our employee handbook states that if I had called in two hours prior with a doctors note that I am covered (which I did)
Is there any use in fighting this?

Will whoever you talked to when you called in confirm the conversation? If so, I'd take a (polite) shot at it.

IF the situation had been covered by FMLA, the write up would have been illegal. Since it was not covered under FMLA, it's not illegal.

What would have happened had the circumstances been different is not relevant.

Do I agree with how your employer handled it? No, I do not.

Do you have legal recourse? No, you do not. Not unless you can show (and you will only be able to show this with the help of an attorney, and maybe not even then) that the employee handbook is contractual and cannot be varied from under any circumstances.

It's up to you to decide if that's worth it for you over a write up.