Tennessee lawmakers have approved legislation drastically expanding the number of families who can use taxpayer money on private schools regardless of income.

In one of the most hotly-contested questions in modern Tennessee political history, the legislature narrowly approved a $430 million private-school voucher program that critics say will grow quickly to $1 billion and endanger the state’s budget.

Tennessee House and Senate education committees passed the governor’s private-school voucher program Tuesday, speeding the $450 million first-year expense to final votes before week’s end. Senators voted 8-1 to send the measure to the finance committee to be considered Wednesday.