The showdown also left in doubt a deal on wages, benefits and education reforms for 29,000 unionized teachers that negotiators had hoped would end the biggest labor dispute in the United States in a year.
Union President Karen Lewis said some 800 union delegates met on Sunday and decided to go back to consult with rank-and-file members before voting whether to end the walk out.
"There's no trust (of the school district and mayor)," Lewis told a news conference. "So you have a population of people who are frightened of never being able to work for no fault of their own."
Union delegates will reconvene on Tuesday to discuss the feedback from rank-and-file members, Lewis said. Parents should plan for their children to be out of school until at least Wednesday, she said.
No formal vote of delegates was taken, but they were asked to stand up so that the union leadership could get a sense of how many were for and against ending the strike, delegates said.
"A clear majority wanted to stay out. That's why we are staying out," Lewis told a news conference after a three-hour meeting of the delegates.
Emanuel called the strike "illegal" and said he would go to court to seek an injunction to block the strike.
"I will not stand by while the children of Chicago are played as pawns in an internal dispute within a union," Emanuel said, adding that the union walked out over issues that are not subject to a strike under Illinois state law.
Teachers revolted last week against sweeping education reforms sought by Emanuel, especially evaluating teachers based on the standardized test scores of their students. They also fear a wave of neighborhood school closings that could result in mass teacher layoffs. They want a guarantee that laid-off teachers will be "recalled" for other jobs in the district.
"They're still not happy with the evaluations. They're not happy with the recall (provision)," Lewis said of the union delegates.
Before the meeting of delegates on Sunday, Lewis had called the agreement a "good contract." But after the decision to extend the strike she backtracked, saying: "This is not a good deal. This is the deal we got."
Emanuel's chief negotiator, School Board President David Vitale, said the union should allow children to go back to school while the two sides go through the process of approval of the agreement.
"We are extremely disappointed that after 10 months of discussion reaching an honest and fair compromise that (the union) decided to continue their strike of choice and keep our children out of the classroom," Vitale said.
During the first week of the strike, parents and Chicago voters appeared to back the union, with some parents and students joining boisterous rallies and opinion polls showing support. A key question is whether the extension of the strike will anger some parents and raise support for Emanuel's efforts to end it.
Both sides appeared to win some concessions, according to details of the tentative agreement released by the parties.
Emanuel compromised on the design of the first update of the evaluation system for Chicago teachers in 40 years. He agreed to phase in the new plan over several years and reduced the weighting of standardized test results in reviewing teachers.
Teachers won some job-security protections and prevented the introduction of merit pay in their contract.
The Chicago strike has shone a bright light on a fierce national debate over how to reform failing inner-city schools. The union believes that more money and resources should be given to neighborhood public schools to help them improve.
Emanuel and a legion of financiers and philanthropists believe that failing schools should be closed and reopened with new staff and principals to give the students the best chance of improving academically.
In Chicago, more than 80 neighborhood schools have been closed in the last decade as the enrollment has declined by about 20 percent. The Chicago Tribune reported last week that another 120 of about 600 city public schools could be closed.
At the same time, 96 so-called charter schools have been opened. Charters are controversial because they are publicly funded but non-union and not subject to some public school rules and regulations. Their record of improving student academic performance is mixed, studies show.
Lewis and the union argue that charters are undermining public education.
The agreement calls for a 3 percent pay raise for teachers this year and 2 percent in each of the next two years. If the agreement is extended for an optional fourth year, teachers get a 3 percent increase. The increases will result in an average 17.6 increase over four years, the district said.
The deal could worsen the Chicago Public Schools financial crisis. Emanuel said the contract will cost $295 million over four years, or $74 million per year.
Debt rating agencies had previously warned that the new agreement with teachers could bust the school district budget and lead to a downgrade of its credit rating.
The district has drained all its financial reserves to cover an expected budget deficit over the next year and has levied the maximum property tax allowed by law.
Lewis said teachers also fear that when the strike ends, Emanuel will soon announce the closing of scores of schools to save money to pay for the new contract with teachers and to make room for opening more charter schools.
Teachers won a concession from Emanuel that half of all teachers hired by the district must be union members laid off from school closings.
