Here is a closer look:
Remaining issues • The district offered a cost-of-living raise of 2 percent a year for four years, which the union said was unacceptable especially after Mayor Rahm Emanuel last year canceled a previously negotiated 4 percent raise, citing budget problems. A school district spokeswoman has said that raise will not be made up and the district will not address it in negotiations. The union has lowered the amount it's asking for, but has not said what its counterproposal is now. Only weeks ago, it sought a 19 percent raise in the first year of the contract.
The union also is concerned about raises based on teacher experience and education. It has said the district agreed to retain language allowing raises based on experience, called step increases, but it would not actually pay the money now. Keeping the language in the contract, though, could be important for teachers in future negotiations.
Teachers also are concerned about new teacher evaluations, health benefits and how a longer school day for students is being implemented.
Hard feelings • Negotiations did not get off to a good start. The union and school district began negotiating in November on a contract that was to expire seven months later, in June. Things heated up in May, when teachers picketed over a lack of progress on talks. Then in June, 90 percent of teachers voted to authorize a strike if a contract wasn't reached over the summer.
It all began when Emanuel last year asked the union to re-open its existing contract and accept 2 percent pay raises in exchange for lengthening the day by 90 minutes. The union refused, noting he'd already rescinded 4 percent raises over the summer. Emanuel, who had won legislative approval to lengthen the school day, then attempted to go around the union by asking individual schools to waive the contract and add 90 minutes to the day until the Illinois Educational Labor Relations Board told him he couldn't.
The mayor also angered teachers by publicly declaring that students were getting "the shaft," though he since has toned down his rhetoric.
Mixed messages • In July, there appeared to be a big breakthrough in negotiations when the district agreed to hire almost 500 laid-off teachers so students would have a longer day but current teachers wouldn't. Both sides expressed optimism that a deal could be reached, but the hires didn't give talks the lift many expected.
Since then, the optimism gave way to a 10-day notice to strike, which goes into effect Monday. Even as the union complained about a virtual stalemate, the district insisted talks were progressing. On Friday, the union president said the talks had taken a "turn for the better," while her spokeswoman hours later issued a statement saying the two sides remained far apart on pay and job security.
If the teachers do go on strike, the city has set aside $25 million to keep 144 schools open between 8:30 a.m. and 12:30 p.m. Staffed by non-union and central office workers, the schools would provide activities such as independent reading and athletics, along with two meals.
What's at stake • Behind the posturing on both sides is a tense showdown between Emanuel and the teachers, with possible ramifications beyond Chicago at a time when most unions have seen their power slip dramatically.
Emanuel, a nationally recognized, powerful Democrat who has taken a tough stance against other city unions, had made good on his promise of a longer school day, and he could get more concessions from teachers while the district faces a nearly $700 million deficit. But he also risks souring relations with the unions and would be the first big-city mayor to deal with a strike since Detroit teachers walked in 2006. The last Chicago strike was 1987.
Meanwhile, teachers and the union believe they have to take a tough stand now so they don't lose ground on pay raises and have a say in job security issues, especially as teacher evaluations are tied more closely to student performance. They're also aware that their struggle is being watched by other unions around the country, many of which feel as if they're under attack.