UPDATE: Teacher strike to go into second day...



For the first time in 25 years, teachers in the country's third-largest public school system hit the picket line.



After a weekend of unsuccessful 11th hour contract negotiations, the Chicago Teachers Union made good on its promise to walk out on more than 350,000 students at 675 schools.



"We have failed to reach an agreement that will prevent a labor strike," Chicago Teachers Union President Karen Lewis said.



The strike follows more than a year of slow, contentious negotiations over salary, health benefits and job security after the school board unanimously voted last year to cancel teachers' 4 percent pay hike in the final year of their contract.



CPS went into full-on strike mode Monday, enacting a plan to keep 144 schools open from 8:30 a.m. to 12:30 p.m. And after a violent Chicago summer, police Supt. Garry McCarthy said he's "emptying our offices" to patrol the thousands of unsupervised kids on the streets.



"This is a difficult decision and one we hoped we could've avoided," Lewis said Sunday. "Throughout these negotiations, we've remained hopeful but determined. We must do things differently in this city if we are to provide students the education they so rightfully deserve."



Moments earlier, Chicago School Board President David Vitale said more than 20 offers had been made to teachers throughout the talks in hopes of preventing a strike.



Still, there was no deal.



"There's only so much money in the system," Vitale said. "There's only so many things we can do that are available to us that we actually believe will not hurt the educational agenda that we think is best for our children."



Chicago teachers make an average of between $69,470 and $76,000 per year, second highest to New York City. Vitale said the deal CPS put on the table includes a 16 percent average salary increase.

"Recognizing the board's fiscal woes," Lewis said the two sides were not far apart on compensation, which had previously been a major sticking point. Issues preventing a deal Sunday night were health benefits, the teacher evaluation system and job security.



More than 26,000 teachers and support staff began hitting the picket lines Monday morning, while the school district and parents made plans for keeping students safe and occupied during the day. Nearly 150 schools will be open for a half day, as will 60 churches. The Chicago Park District and the YMCA will offer day-camps.



Lewis said talks would continue throughout the strike, but she said time had not yet been scheduled Sunday night as to when the two sides will next meet.



The strike sets up a historic confrontation between Mayor Rahm Emanuel, President Barack Obama's former top White House aide, and organized labor in the president's home city.



"I am disappointed that we have come to this point given that all the other parties acknowledged how close we are, because this is is a strike of choice," said Emanuel. "And because of how close we are, it is a strike that is unnecessary."



The work stoppage could hurt relations between Obama's Democrats and national labor unions, who are among the biggest financial supporters of the Democratic Party, and will be needed by the party to help get out the vote in the November 6 election.



While Emanuel has not attended the talks, he and Lewis have clashed. She has accused him of being a bully and using profanity in private meetings.



Teachers walked off the job for 19 days in October 1987. Prior to that, there had been nine strikes between 1969 and 1987.



Charter Schools Open Monday



Students who attend charter schools should go to school, officials reminded Sunday.



"We think our parents have gotten the message. We think our kids have gotten the message, but we wanted to make sure that we were very clear to every person who lives in Chicago that charter schools will be open tomorrow," said Beth Purvis, the CEO of Chicago International Charter Schools.



There are about 45,000 charter school students in the city -- about 12 percent of the city's total student enrollment.

Chicago Mayor Rahm Emanuel says he's "disappointed" by teacher strike given how close sides are to resolution.

NBC Chicago has an array of reporters and producers covering the Chicago teacher strike. Check our live blog for continuous coverage and updates throughout the strike.