CHICAGO — Chicago teachers uncomfortable with a tentative contract offer decided Sunday to remain on strike, insisting they need more time before deciding whether to end an acrimonious standoff with Mayor Rahm Emanuel that will keep 350,000 students out of class for at least two more days.

Emanuel fired back Sunday night by instructing city attorneys to seek a court order forcing Chicago Teachers Union members back into classrooms. ‘‘This was a strike of choice and is now a delay of choice that is wrong for our children,’’ he said in a statement.

Presented with a choice on whether to ask members to vote on a contract that union president Karen Lewis had at one point called ‘‘a fight for the very soul of public education,’’ the union’s 800-member House of Delegates told their leaders they needed more time to talk to the rank and file before ending the city’s first teachers strike in 25 years.

Teachers had only a few hours to review a summary of a proposed settlement worked out over the weekend with officials from the nation’s third largest school district. That wasn’t enough time, they said, to digest a complicated contract that addresses two issues central to the debate about the future of public education across the nation: teacher evaluations and job security.

The union will meet Tuesday, after the end of the Rosh Hashana, the Jewish new year.

‘‘We felt more comfortable being able to take back what’s on the table and let our constituents look at it and digest it,’’ said Dean Refakes, a physical education teacher at Gompers Elementary School.

That timeline, however, means the earliest classes could resume would be Wednesday. That frustrated both Emanuel and some parents, who learned late at night a week ago Sunday that last-minute negotiations had failed to produce a contract and that the strike was on.

‘‘I think a week is a long time to be wasting time. Another week would be murder. I don’t think it’s right,’’ said Beatriz Fierro, the mother of a fifth grader. ‘‘They should be back in school.’’

Other parents continued to stand with the union. As teachers walked picket lines in the past week and rallied Saturday in a park near downtown, they were joined by parents who have had to scramble to find baby-sitters or a supervised place for children to pass the time.

‘‘As much as we want our kids back in school, teachers need to make sure they have dotted all their I’s and crossed their T’s,’’ said Becky Malone, mother of a second-grader and fourth-grader. ‘‘What’s the point of going on strike if you don’t get everything you need out of it? For parents, it’ll be no more of a challenge than it’s been in the past week.’’

Emanuel did not appear at a brief news conference Sunday night with city school board president David Vitale, who said 147 schools staffed with nonunion workers and central office employees would be open Monday for students who are dependent on school meals.

But in a statement, Emanuel was typically blunt. He accused the union of using the city’s students as ‘‘pawns in an internal dispute.’’ He said the strike was illegal because it endangers the health and safety of students and concerned issues — evaluations, layoffs, and recall rights — that Illinois state law says cannot be grounds for a work stoppage.

‘‘While the union works through its remaining issues, there is no reason why the children of Chicago should not be back in the classroom as they had been for weeks while negotiators worked through these same issues,’’ he said.

The walkout, the first for a major American city in at least six years, canceled classes for students who just returned from summer vacation and forced tens of thousands of parents to find alternatives for idle children, including many whose neighborhoods have been wracked by gang violence in recent months.

With an average salary of $76,000, Chicago teachers are among the highest-paid in the nation. The contract outline calls for annual raises, but it does not restore a 4 percent raise that was rescinded by the mayor last year.

That upset many teachers, said union delegate Susan Hickey, a school social worker. But she said the proposal was ultimately one teachers — who are worried that staying out beyond mid-week will further upset parents — could support.

‘‘Personally I think there’s a lot of us who don’t want to lose the parental support,’’ she said.

Lewis said delegates weren’t yet willing to go back to work while contract language was amended because of distrust between the union and the city, and the fact the settlement on the table remains tentative.