Private school voucher programs raise a number of legal issues, and many have faced court challenges. Voucher programs may violate a state constitution's education clause, including a state's obligation to adequately fund public schools or to provide a uniform system of public schools, and other important state constitutional protections.

Voucher lawsuits have also been based on violations of the First Amendment to the U.S. Constitution as well as state constitutional provisions, known as Blaine Amendments or no-aid clauses, that prohibit public funding of religious institutions. Other voucher lawsuits have focused on students' civil rights guarantees.

PFPS uses the power of litigation as one important tool to scale back and stop private school voucher programs and other diversions of public funds from public schools. There are numerous ways to utilize the legal system to challenge vouchers, including participation as a party to litigation or submission of amicus curiae, or "friend of the court," briefs. In addition to direct participation in court challenges, PFPS seeks to assist local, state, and national partners and networks in their efforts to challenge vouchers in court.