Is it legal to lay off someone due to medical issues?

As a general rule, an employer may fire an employee who misses work if that person did not use accrued leave (e.g. sick time or PTO) for the absence. The fact is that there is no general right to miss work. However, if both you and your employer met the criteria for coverage under the Family and Medical Leave Act (FMLA), it may be that you had the right to take leave (unpaid) although even in such a case, you generally have to ask for the leave first. Therefore, while you might have some legal recourse, there is very good chance you do not. Accordingly, your discharge was proper

Note: In order to be eligible for FMLA, there are certain criteria that must be met: the company at which you worked must have had at least 50 employees within a 75-mile radius; you must have worked at least 12 months (which do not have to be consecutive) for the employer and you must also have worked at least 1,250 hours during the 12 months immediately before the date FMLA leave is to begin. Further, an employer need not count employment prior to a break in service of 7 years or more unless there was a written agreement between the employer and employee to rehire the employee or the break in service was due to fulfillment of military service in the National Guard or Reserves.