Bloomberg is investing $2.5 million in “no” efforts.

Former New York Mayor Michael Bloomberg donated $2.5 million to a group trying to get the ballot question overturned eliminate the MCAS test as a graduation requirementmaking a significant contribution to a heated campaign just before Election Day.

The largest contribution is Bloomberg’s seven-figure donation “Vote No for 2” campaign. received and represents more than half of the $4.8 million she reported raising this election campaign, status data shows.

This isn’t the first time a billionaire has donated money to a Massachusetts election campaign. In 2016, Bloomberg donated $490,000 to a failed ballot question it would expand charter schools in Massachusetts.

If approved by voters, Question 2 would repeal a provision of the state’s landmark 1993 education law that makes earning a high school diploma contingent on students passing MCAS exams in English, math and science. In its place, the ballot measure would establish a new mandate: Students would have to complete coursework certified by their districts in subjects that meet state academic standards. The state could add new entities to this list.

The Massachusetts Teachers Associationthe state’s largest teachers union is pushing the initiative, arguing that the mandate causes schools to focus too much on test preparation and MCAS subjects. It also argues that the requirement causes too much anxiety among students, unfairly penalizes students who perform poorly on the exam and is potentially discriminatory.

Opponents of the issue, including Gov. Maura Healey, argued that the MCAS completion requirement helped grow Massachusetts schools from the middle of the pack across the country to the top. The business-backed group opposition to the initiative has drawn contributions from other wealthy donors, including New Balance CEO Jim Davis, who gave $250,000 this month, and Bain Capital’s Paul Edgerley, who gave $100,000.

But Bloomberg is by far the biggest. A Medford resident made a donation on Oct. 22; the campaign revealed this in a report submitted on Friday afternoon.

WBUR first reported contribution.

“Mike Bloomberg has been a staunch advocate for issues affecting children, such as reducing gun violence and improving education,” Dominic Sloweycq, spokesman for the Vote No on 2 campaign, said in a statement. “We appreciate his support of our broad and bipartisan coalition of educators, parents, education and business organizations, and elected officials in opposition to Question 2.”

Globe staff member James Vaznis contributed to this report.

Matt Stout can be reached at [email protected]. Follow him @mattpstout.