At a hearing Monday, Boston city councilors argued that lifting the cap on charter schools could have disastrous consequences for the city’s schools and its future.

The trouble has to do mostly with the way charter schools are funded.

When students leave a traditional school district for charters, cities have to send a set amount of funding per pupil. By law, the commonwealth of Massachusetts is supposed to reimburse districts for the missing funds.

Data from City of Boston Office of Budget Management (Courtesy Boston Public Schools report)

But for the past three years, the state Legislature has failed to meet that obligation at the mandated level. And that means Boston and other cities have been forced to take school funding from elsewhere in the budget — and to forgo certain services.

“There are an incredible number of shortfalls, whether it’s librarians, school psychologists, guidance counselors,” said Councilor Annissa Essaibi George, who called the hearing and who taught in Boston Public Schools for 13 years. “That problem is only going to be magnified should Question 2 be passed.”

David Sweeney, the city’s chief financial officer, projects that even moderate growth in charter school attendance — around 7,000 new students over 10 years — would increase the city’s charter assessment by 16 percent per year, far outpacing projected growth in revenue.

And if Question 2 passes, the gap could grow much wider. The worst-case scenario projections hold that the bill could top $800 million by 2028.

“This is like ‘Mad Max’ — an apocalyptic change relative to education, and actually to the city,” said Councilor Tito Jackson, who has been a vocal opponent of Question 2 for months. “I can’t imagine sending $800 million to organizations that we have zero control [over].”

Sam Tyler, president of the independent Boston Municipal Research Bureau, expressed less concern.

He favors increasing the number of charter schools but acknowledged that Question 2 is a “blunt instrument” and that city and state officials would have to act to mitigate budget shortfalls if it passes.

As the hearing drew to a close, you could hear dozens of the city’s first early voters waiting to cast their ballots in the City Hall lobby.