PHOENIX (AP) — Years before the demands for higher teacher pay led to a school walkout in Arizona, one of the state’s high-profile charter schools found a way to subsidized teachers’ income: push parents to pay.

Basis Charter Schools Inc., which operates 20 public charter schools in the state with more than 900 teachers, asks parents to make donations to benefit its teachers, The Arizona Republic reported Monday.

Basis receives per-student funding from the state and cannot charge tuition as a public charter school. It is not illegal for schools to request donations from parents.

The nonprofit company’s school in Scottsdale requests at least $1,500 per child each year, according to records obtained by the newspaper. A pledge card from the school noted that the donated money “represents a fraction of the annual cost of a top private school education.”

Basis schools received about $84 million in state funding last year. The charter company also received about $5 million in donations, according to its records.

Teachers who work in Basis schools are contracted through Basis.ed, a private company owned by Basis founders Michael and Olga Block, according to Arizona Corporation Commission records.

While the average pay for Arizona public school teachers is a little over $48,000, the average Basis teacher salary is about $41,000, according to Arizona Department of Education records.