Can fees be based on ability to pay or must I offer the same discount to all uninsured patients?

You can have a sliding scale. The key is to offer the sliding discount to everyone who qualifies; that is, be consistent. But it's the policy that needs to be consistent, not the actual percentages. The issue of providing free and reduced-price care to the poor and uninsured has become a big one for many practices, as many employers are dropping coverage, reducing benefits, or just laying people off.