St. Paul Public Schools classes are canceled Tuesday because of a teachers strike, the school district said early Tuesday morning.

The district notified parents via Twitter at 3:30 a.m. The St. Paul Federation of Educators said in its own tweet that it would begin picketing at 7 a.m.

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Negotiators for the St. Paul Public Schools and the union representing its teachers continued to talk into the night Monday in hopes of averting a strike — the district’s first since 1946.

About 9:45 p.m., the district texted parents to say it remained hopeful an agreement could be reached, but that if a strike were called, it would inform parents and staff by 5 a.m. Tuesday.

The walkout tentatively set for Tuesday would cancel classes and force parents to make alternate plans for their children. A strike also would place the district at the center of a national movement of educators organizing to fight for better pay and greater resources for students — many of whom they say need mental health support.

Monday marked the sixth consecutive day of mediation. The union — the St. Paul Federation of Educators (SPFE) — began the day saying there had been “no significant movement” on its priorities while the district sought to stand firm on budget parameters set for all of its bargaining units.

Late in the afternoon, the union’s executive board unanimously rejected Superintendent Joe Gothard’s request for arbitration, which he described as a way to “avoid a strike and keep our students in school.”

The union said then it was prepared to go all night. Nick Faber, the federation’s president, said it would be up to the district to cancel classes.

Initially, the SPFE pursued mental health teams in every building — 300 more employees by the district’s count at a cost of $30 million a year — as well as 50 interpreters to work with students and families plus additional staff to work with special-education students.

On Sunday, Marny Xiong, the school board’s chairwoman, released a statement saying the board agreed students need additional support, but members also had to manage the budget.

She said SPFE’s demands would jeopardize resources for other unions in the district, and force cuts to programs and other needs.

“The reality is that there isn’t a secret pot of money hiding somewhere,” she wrote.

The union already had begun mobilizing community support. A Facebook group, “Rise up with Saint Paul Educators,” was created and included plans for a march and rally that would begin at 3 p.m. Tuesday at Global Arts Plus upper campus, 810 Palace Av., and end at district headquarters.

Among the speakers set to attend were state and national union leaders who at a Monday morning news conference commended the SPFE for recognizing that a collective voice was needed to get children the services they need.

They spoke, too, of the political momentum building across the country, prompting a reporter to ask if they planned to give input on a federation decision to strike.

“The ‘Local’ is the power here,” replied Lily Eskelsen Garcia, president of the National Education Association. “We’re not pulling any strings here. They are the ones sitting at the table.”

The SPFE has listed some child care options on its website — www.spfe28.org — including three St. Paul Boys and Girls Club locations that the union says would waive admission fees during the strike.

They would serve breakfast and lunch and provide academic programs.

The Como Park Zoo and YMCA would offer child care programs, and Loaves and Fishes would serve meals at various church locations in the area, the union said.

According to the city of St. Paul’s website, the Parks & Recreation Department and public libraries also would offer resources to students. Recreation centers that usually open at 2 p.m. instead would open at 1 p.m. Public libraries would maintain regular hours. Some recreation centers and libraries also would provide meals, the city said.

Katrina Pross, a University of Minnesota student on assignment for the Star Tribune, contributed to this report.