A group that funded the failed campaign to expand charter schools in Massachusetts last year has been found to have illegally hidden the identities of wealthy donors who gave to the Question 2 effort.

The Massachusetts Office of Campaign and Political Finance fined the group Families for Excellent Schools $426,466 for failing to disclose the donors who helped bankroll the pro-charter effort, including two members of Gov. Charlie Baker's administration.

The Associated Press reported that it is the highest campaign-finance fine in state history.

Baker said the members of his administration who donated to the group followed the law and that the wrongdoing was Families for Excellent Schools' decision not to disclose the donors.

"It's up to the group to make the decision with respect to when they publicly list their donors, and OCPF did an investigation, concluded that they violated the law and fined them appropriately for that. But that's on the group," Baker told reporters Monday.

UMass Boston Political Science professor and WGBH contributor Maurice Cunningham has been investigating the funding that backed up the pro-charter movement for months on the MassPoliticsProfs blog.

“Today’s agreement between the Office of Campaign and Political Finance and Families for Excellent Schools is great news for the citizens of Massachusetts," Cunningham wrote Monday.

"Voters deserve the right to know who is spending millions to influence their votes, and this decision upholds that right. It also shows that Families for Excellent Schools, despite its claim to be a family education reform group, is in fact a dark money political operation."

Baker said he's known about the investigation for only a few days and is glad the matter is settled. 

Baker's cabinet-level IT chief Mark Nunnelly gave $275,000 to the group, according to the Boston Globe. 

“A quality education is essential to developing a skilled workforce for the future. For 25 years, my wife and I have been dedicated supporters of Massachusetts public schools and all they do to maintain our position as the national leader in public education." Nunnelly wrote in a statement distributed by Baker's office.