The Boston Teachers Union walked out on contract negotiations with the School Department on Tuesday to protest the public release of proposed schedule changes to the school calendar that are part of ongoing collective bargaining, according to the union president.

In a March 11 memo to the School Committee, Superintendent Tommy Changsuggested eliminating the district’s February vacation and expanding its winter holiday break, as well as moving the start of school to the week before Labor Day in 2017 and to two weeks before the holiday for 2018.

Copies of the memo were distributed at the School Committee meeting last week. Some parents have since expressed reservations about changing a calendar that affects vacations, summer jobs, and child-care planning for tens of thousands of families.

Because any change to the district calendar is subject to negotiation with the union, public disclosure of the plan violates confidentiality rules agreed upon by both parties, Richard Stutman, the union’s president, said Wednesday.

Stutman said union representatives sat at the negotiating table Tuesday only long enough to convey their frustration that Chang had violated their agreement.

“We voiced our concerns, and then we walked out,’’ he said.

Stutman declined to describe the district’s response, and a School Department spokesman declined to comment on the walkout.

Stutman said that after the scheduling proposal became public, the union received calls from members, “almost all of them insulted and rejecting the proposal.’’

“The members don’t like being blindsided. The members don’t like the thought of losing February [vacation]; I’d say that’s probably 100 percent. And I’d say 90 percent don’t like the idea of starting on Aug. 22 [for 2018],’’ he said.

Stutman also was critical of the district’s plan, reported in The Globe, to survey parents on the viability of the calendar change, which he described as an effort to buttress its argument in favor of the proposed shift.

He questioned why Chang made changing the calendar a priority when other issues are more pressing, he said.

“Having clean schools, clean toilets, hot and cold running water every day . . . is more important than any one of the items that he has proposed,’’ Stutman said. “Having lower class sizes is more important. Having students work in a safe and secure, clean environment is more important.’’

He said he had spoken to Chang on Wednesday and plans to speak with him again soon. Stutman said he harbors no resentment and wants to return to the negotiating table to work collaboratively and respectfully.

“We had a very nice conversation this morning,’’ he said.

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Jeremy C. Fox can be reached at jeremy.fox@globe.com. Follow him on Twitter @jeremycfox.