25,000 Chicago teachers head to the picket lines.
Teachers in the country's third-largest public school system hit the picket line Monday.
After a weekend of unsuccessful contract negotiations, the Chicago Teachers Union made good on its promise to walk out on more than 400,000 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.
"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."
He said the deal they put on the table would cover four years and cost the city $400 million.