Can my employer fire me for failure to report to work while on sick leave.

1) As a general matter, if you took the time off in violation of company policy (e.g. they do not have a "call out" policy to take time off for illness) and/or without using paid time off that you had earned (e.g. sick days) for the absence, you may be fired. The law does not require employers to let employees miss work for being sick, unless a) there is, and the employee complies with, a company policy allowing it; b) the employee uses sick days; or c) the company is covered by, the employee is eligible for, the illness qualifies for, and the employee properly uses FMLA leave. Absences, other than a), b), or c), can result in termination, even when there is  doctor's advice to miss work.
2) Even if you technically complied with company sick leave policy or used sick days, if the company reasonably, on the evidence, believes that you lied and used sick leave or sick days when you were not sick--for example, used them to get a vacation which had been denied to you--then you could be terminated for that: sick leave can only be used when actually sick. If you took off the exact days that you had been denied for vacation leave, that looks very much like you were using sick days to get a vacation when you otherwise could not. Unless you can prove the illness and the medical advice that you take those exact days off (e.g. by documentation from a doctor), the employer is justified as treating what you did as an unauthorized absence and an attempt to get around the company's decision about your vacation, and terminate you on that basis.