BOSTON — Gov. Charlie Baker is defending a $100,000 donation by the chairman of the Massachusetts board of education to a group pushing a pro-charter school ballot question.

The Republican told reporters Monday that Board of Elementary and Secondary Education Chairman Paul Sagan sought and won the approval of the state Ethics Commission before making the donation. Baker, a longtime supporter of charter schools, appointed Sagan to the position last year.

“It’s a nothing-burger,” Baker said when asked about the donation. “Are we going to get into the business of saying every private citizen in Massachusetts has no ability to do anything associated with their private position?”

Opponents of the charter school question are demanding Sagan’s resignation.

Juan Cofield, chairman of the Campaign to Save Our Public Schools, said the donation will impair Sagan’s judgment and impartiality.

“How can Sagan be trusted to properly regulate charter schools when he’s so invested in expanding them? The chairman needs to step down immediately,” Cofield said in a statement.

Question 2 would allow for up to 12 new or expanded charter schools each year outside of existing state caps.

Sagan said in a statement that he was happy to disclose his contribution. He described himself as “a dedicated supporter” of all of public schools including traditional district public schools and public charter schools.

“It is an honor to serve as Chairman of the Board of Elementary and Secondary to Education and I am thrilled to work toward maintaining Massachusetts’ position as a national leader in public education,” Sagan said.

The donation also drew criticism from the chairman of the Massachusetts Democratic Party who said the donation “calls into question the governor’s judgment on who best serves the people of the commonwealth.”

“As chairman of the Massachusetts Board of Elementary and Secondary Education, Mr. Sagan has a duty to fulfill that position in an unbiased manner, free from personal opinion,” Massachusetts Democratic Party Chairman Tom McGee said in a statement, adding that the donation “suggests an inappropriate bias and, at the very least, shows poor judgment.”

The question is one of the most contentious on the November ballot.

Supporters and opponents have pulled in nearly $19 million in contributions.

Charter school activists raised $12 million, according to reports filed late Friday with the state Office of Campaign and Political Finance. That’s nearly double the $6.8 million raised by opponents of the question, including teachers unions.

Donors to the pro-charter school campaign include two prominent billionaires — former New York City Mayor Michael Bloomberg who contributed $240,000 and Jim Walton of Arizona, the son of Walmart founder Sam Walton, who contributed more than $1.1 million.

Another $5.5 million in direct contributions came from the New York City-based Families For Excellent Schools Advocacy, Inc.

The three biggest donors to the group Save Our Public Schools, which opposes the ballot question, are teachers unions.

The Massachusetts Teachers Association directly contributed nearly $4.2 million. The Boston- and Washington-based American Federation of Teachers gave more than $700,000. The Washington-based National Education Association contributed $1.9 million.