They're contracts, so generally contract law. Although such contracts would have to be careful to not run afoul of employment laws, or laws against slavery. It

They're contracts, so generally contract law. Although such contracts would have to be careful to not run afoul of employment laws, or laws against slavery. It seems income sharing agreements typically include clauses which mitigate their risk of becoming invalid as voluntary slavery, such as limited time, a minimum income threshold, and buyout options. They could also be structured as a debt, with a payment structure based on income. Potentially bankruptcy law would affect their interpretation also.