The big-money ballot battle over expanding the number of charter schools in Massachusetts is coming to a TV near you starting Tuesday. The teachers’ union-backed group opposing a November referendum that would allow for the creation or expansion of up to 12 charter schools per year is launching a potent 30-second spot.

“Four-hundred million dollars,’’ says a female voice over a black-and-white video of young people in a hallway with lockers. “That’s how much charter schools will drain from Massachusetts public schools this year. Four-hundred million siphoned from local districts that desperately need it.’’

It concludes with the narrator saying: “Let’s improve public schools for all students, not just a select few. Vote no on Question 2.’’

Steve Crawford, a spokesman for the Campaign to Save Our Public Schools, the organization behind the ad, said the spot will be backed by more than $800,000 worth of spending this month on Boston-area television.

According to a disclosure on the ad, the top contributors are teachers’ unions: The Massachusetts Teachers Association, the American Federation of Teachers, and the National Education Association.

Jim Conroy, an adviser to the pro-charter campaign, hit back. He said the state’s “best in the nation charter schools are free and public schools that provide great results for students stuck in failing districts.’’

He said the “special interests opposing Question 2 are more interested in peddling blatant mistruths to protect their status quo than they are about expanding access to these proven successful schools for the students who need it most.’’

If voters approve it, the measure will mean significant additions to the state’s existing count of more than 80 charter schools.

Watch the ad at www.bit.ly/MABallotQAd.

Joshua Miller