New York City has reached the legal limit of charter schools, which has prompted a big push by charter advocates to raise the cap.

Albany needs to stand firm.

The push to expand is driven by big, anti-union charter chains backed by Wall Street money. If state lawmakers waver, we will be on our way to creating a parallel — but unregulated and discriminatory — school system in New York City. Two community school districts — District 5 in Harlem and District 16 in Bedford-Stuyvesant — already have or soon will have a majority of students enrolled in charter schools.

The charter chains have figured out a way to game the system, which will propel their growth for years to come even if the current cap remains in place. Success Academy Charter Schools, for example, commonly receive approval for an elementary school, but then expand beyond elementary school grades until a school becomes K–8 or K–12, all under the same original charter. It’s essentially up to three schools for one charter. Senate bill 5950, introduced by Senate Education Committee Chair Shelley Mayer, would close this loophole.

Success Academy alone is authorized under current charter rules to add nearly 10,000 seats, while Achievement First and KIPP can add 3,000 seats each.

In California, where there is no cap, an ever-growing charter sector has been draining funds from traditional public schools for decades. California now has more than 1,000 charter schools. About 20 percent of the Los Angeles district’s 500,000 students attend charter schools, which operate with little accountability. A 2016 report found more than 20 percent of charter schools in California have enrollment policies that violate state and federal law. California public schools, meanwhile, struggle to teach the students with the greatest challenges as funding diminishes.

That’s why when Los Angeles teachers walked out of their classrooms earlier this year they called for a moratorium on charter schools and greater transparency in charter operations.

California illustrates the repercussions of unchecked charter growth. Similar issues, albeit on a smaller scale, are playing out here in New York City. Albany should not wait until the New York City school system reaches the tipping point to take action.