At this writing, only six municipalities and two states require (or will soon require) resident employers to provide employee sick leave benefits, whether with or without sick pay.*
About 43 percent of U.S. workers do not have paid sick leave benefits, while nearly 75 percent of low-wage workers do not have sick leave benefits at all.
Elsewhere, providing employee sick leave benefits is voluntary for employers, as it is with many benefits that employers have traditionally provided.
Some employers provide sick leave anyway, to attract and retain employees. Some of those also voluntarily include accrued sick pay in employees' final paychecks, as incentive to reduce sick leave abuse.
Under the Federal Family and Medical Leave Act (FMLA), your employee rights might entitle you to take sick leave to care for yourself or family members, without losing your job and benefits. But, to clarify, FMLA leave is not the traditional employer-provided sick leave benefit addressed in this article and the Act does not require your employer to issue sick pay to you while you're on such leave.
If your employer does provide a traditional sick leave benefit, then you are generally entitled to it if you adhere to the related policies. Because it's a voluntary benefit, your employer may dictate the terms of sick leave, such as in an employee handbook. For example, to avoid disciplinary action for missing work due to illness, your employer likely may require you by policy to submit a written excuse from a doctor.
If you violate an employee sick leave policy, then your employer likely may take disciplinary action, such as depriving you of sick pay or worse, firing you. But the courts typically consider all factors involved, to decide whether or not employers really had good cause to fire employees for company policy violation. Consult an attorney about that.
Read About Employee Benefits for information regarding avenues of relief, should your employer deprive you of the sick leave benefit or any other employee benefit to which you're rightfully entitled.
Update: On September 7 (Labor Day), 2015, President Obama signed an Executive Order requiring certain government contractors and subcontractors to grant at least seven days of paid sick leave to their employees per year.