A new school funding lawsuit filed upstate could be a boon for nearly 70 charter schools in the five boroughs.

The lawsuit, filed Monday by four families from Buffalo and one family from Rochester, claims that the state shortchanges students in charter schools by not providing money for space. And while the complaint focuses on funding disparities in upstate cities, their claims would also apply to dozens of New York City charter schools that still aren’t guaranteed facilities funding.

The legal attack represents the latest front in a lengthy battle over charter school facilities funding, which has its roots in the 1998 law that first allowed charter schools to open in New York. Charter schools do receive some state funding, but they weren’t given access to the state’s building aid program, which subsidizes district school construction projects. When schools opened in private facilities, they had to set aside a chunk of their operating budget—meant for teachers and school supplies—toward expenses like rent, security, maintenance, and renovations.

In New York City, those costs can add up. Brooklyn Prospect Charter School Executive Director Daniel Rubenstein told Chalkbeat earlier this year that he had to set aside a little less than 20 percent of his $13 million budget to replace fire alarms, upgrade bathrooms and install a new science lab in addition to paying rent and other facilities expenses.

Most of the nearly 200 charter schools that opened under Mayor Michael Bloomberg received free space in city-owned buildings. But 68 charter schools, serving 25,000 students, operate in private buildings and spend, according to one tally, an extra $2,300 for every student on facilities.

This year’s state budget deal included a law that guarantees access to facilities for new and expanding charter schools in New York City. The deal was hailed as a big win for charter schools, but it did little for schools already open in private space. (More recently, some city charter schools, including the one Rubenstein runs, have said the law does apply to them and have applied for space.)

The law also did not address more than 50 charter schools outside of the city that operate in private space, where facilities costs are lower but still a heavy burden. Charter schools in western and central New York, for instance, spend up to $1,600 on facilities for every student, according to a report by the Northeast Charter School Network, an advocacy group that is part of the lawsuit.

The lawsuit also cites a study of funding disparities between charter schools and district schools that showed big gaps for charters in upstates cities. In Buffalo, for instance, charters receive $9,811 less for its students on average than district schools, a gap of more than 40 percent, the lawsuit states.

By filing a lawsuit, the parents and the charter advocacy group are following a strategy increasingly being employed by groups seeking to challenge state laws supported by teachers unions, like teacher job protection laws.

“We were really hopeful last session that they’d put a fix in to help charters statewide,” said Andrea Rogers, policy director of NECSN, referring to the lobbying campaign waged around access to facilities. “It did do a lot to protect the charter movement in New York City, but not all schools got the relief. So we need to take another approach.”

But increasing funds to charter schools could mean diverting money from district schools that are still struggling to recover from years of budget cuts. Opponents say that is unnecessary because charter schools can also tap private donors for a wide range of support.

Alliance for Quality Education advocacy director Zakiyah Ansari, an ally of teachers unions and Mayor Bill de Blasio, said that lawmakers should focus first on fulfilling the terms of a 2006 lawsuit settlement that was supposed to provide more funds for schools in poor districts.

“We are $5.9 billion behind on the Campaign for Fiscal Equity commitment, and this proposal will only divert more money away from public schools, at the expense of our children,” Ansari said.