The union representing 3,700 St. Paul teachers and school support staff members voted overwhelmingly Wednesday to authorize a strike against the school district.

The St. Paul Federation of Teachers also announced it was serving notice on Thursday of its intent to strike, meaning a walkout could occur in 10 days.

If a strike occurs, all classes, including K-12 and preschool, would be canceled, with students possibly having to make up missed days during the summer, the district said in a statement.

The vote brings new urgency to mediation sessions scheduled for Friday and Wednesday. At issue is whether the district has the resources to pay for proposals — class-size caps and increased support staff, among them — that it generally supports but contends could be too costly at a time of enrollment declines and budget shortfalls.

"Nobody wants to go on strike, and we will do everything in our power to prevent one," Nick Faber, the union's president, said in a statement. "However, we are going to fight for what our students need and not apologize for working to create the schools St. Paul children deserve."

Superintendent Joe Gothard said: "I am disappointed by the vote and concerned for all our families who will feel the impact first. Still, I remain hopeful we can move forward on additional agreements to avoid disruptions to our students, staff and families."

The school board issued a statement saying that while differences between the two sides remain, it does not believe they are irreconcilable.

"We urge SPFT to come back to the negotiating table so we can reach agreement and avoid a strike — which would be divisive and disruptive, and will bring us no closer to an agreement on the contract," the school board said.

The union said that about two-thirds of its members voted, with the strike being backed by 85.1 percent of teachers, 89.5 percent of educational assistants and 82 percent of school and community service professionals.

The federation last called for a strike authorization vote in 1989, when the proposal passed, 2,062 to 254. That walkout was averted when a deal was reached in the final hour. Wednesday's vote could lead to the first strike against St. Paul Public Schools since 1946, when the union apparently was the first in the nation to strike.

Members have been vocal at recent school board meetings about a need to provide additional support to English language learners and expand approaches to discipline that value relationship-building over punitive measures.

"I voted yes to strike because our kids need better supports for English learners, mental health, school nurses, special education and restorative practices," Kristi Herman Hill, a teacher at Washington Technology Magnet School, said. "We can and must do better."

Critics, two of whom, Ian Keith and Roy Magnuson, longtime teachers who have served as federation leaders in the past, say the union has been needlessly divisive in the current negotiations cycle.

School board Chairwoman Zuki Ellis noted that the board shares many of the same aims as the union — from seeking new revenue to improving facilities to hiring new educators and support staff. The difference, she said, is in how best to achieve those goals when resources are limited.

"That's what negotiations are for," Ellis said.

The two sides also have differed on the size of potential teacher pay increases.

As for new revenue, the federation has asked the district to join it in pressuring corporations and nonprofits to contribute financially to the schools, arguing they benefit from tax breaks and other policies that deprive schools of resources. The district wants the union to work with it on an application to enter the state's Q Comp alternative teacher pay program.

Budget season begins shortly, and the district expects another shortfall for 2018-19, although it has yet to state publicly how big it might be.