One of Baltimore’s most successful charter school operators, KIPP, is battling with the Baltimore Teachers Union over the new contract that limits how much teachers are paid, the Baltimore Sun reports.

KIPP schools are known for their extended school days where students are in school for 9 1/2-hours, compared to the more traditional 7 hours. Administrators of KIPP’s Ujima Village Academy say the longer hours are one reason the West Baltimore school has had some of the highest test scores in the state.

The extra hours, however, mean that the faculty at KIPP schools need to get paid more, a raise that would violate the current BTU contract. Currently KIPP (Knowledge is Power Project) is making up the difference out of their own budget, costing them $400 to $500,000 a year, officials there told the Sun. They also said that if the school can’t get the funds needed to support the longer hours that they will shut down by June 30.

KIPP has taken the fight to Annapolis, where a bill has been introduced that would allow faculty at charter schools to have a say in their pay for extended hours and working conditions.