If teachers were to strike this year, they would likely walk off in mid-October, according to reports. View Full Caption DNAinfo/Ted Cox

CHICAGO — With Chicago Public Schools students back in class this week, students and parents are wondering whether teachers will make it through the year without walking off the job.

Rumors of a strike by the Chicago Teachers Union have been swirling since February, when the union's bargaining team rejected a new contract proposal offered by CPS.

In 2012, the last time CPS and union negotiators agreed on a contract, teachers went on strike for the first time in 25 years.

Alex Nitkin talks about the issues separating the teachers union and CPS.

Here's everything you need to know about another possible strike in 2016.

Why are teachers threatening to strike?

When teachers welcomed almost 400,000 students into class on Tuesday, they were entering a second year without a working contract. The last one, negotiated after the 2012 strike, expired on June 30, 2015.

During the last academic year, multiple attempts to hammer out a new contract ended in an impasse, with a wide gulf between CPS proposals and the union's demands.

After union leaders rejected the CPS proposal in February, both sides commissioned a third-party "fact-finding" consultant, which ended up drawing up a contract similar to what CPS had offered. In April, the union's bargaining team rejected that proposal, too.

On Tuesday, union president Karen Lewis published an open letter to teachers vowing that teachers "will not work another year without a contract."

Lewis has said she and her team are trying to avoid a strike, but if CPS negotiators don't meet the union's demands, the city should prepare for one.

What would have to happen in order for teachers to strike?

Under state law, the union would have to file a 10-day strike notice with a state labor board before teachers could walk off the job.

Union leaders already are planning a strike authorization vote, the Tribune reported last week. The vote would likely take place in early October, when the union's House of Delegates — which includes representatives from each of 422 CPS schools — meets in one place.

If the delegates vote in favor of a strike, teachers would likely walk off the job about a week later — in other words, sometime in early- to mid-October.

What kind of contract deal is on the table now?

The contract being offered today closely resembles the one drawn up by the independent consultant in the spring.

It would include an 8.75 percent increase in teachers' wages, plus a cap on new charter schools. It also offers "steps and lanes," automatic bumps in teacher pay that kick in with seniority and experience.

But also included is the so-called "pension pickup," which would require teachers to contribute 9 percent of their salaries into their own pension funds.

By state law, teachers have to put aside 9.4 percent of their yearly salary for their retirement fund. As of now, teachers only put about 2 percent of of their salary into their own pensions, while CPS picks up the other 7 percent or so.

CPS leaders said having teachers pick up the full 9 percent would be a fair sacrifice, given the school system's dire financial situation.

"CPS’ continued objective is to give teachers a fair raise that works within our budget constraints," CPS spokeswoman Emily Bittner wrote in an email, "especially since we just passed a tight budget that included significant tax hikes on Chicago homeowners, Central Office staffing reductions and revenue from Springfield."

The proposed pay raise and "modest" new health care benefits "more than offset the gradual phaseout of the pension pickup," Bittner wrote.

Why won't the teacher's union accept the deal?

CPS officials say they're offering a net increase in teachers' take-home pay, but union leaders don't see it that way.

For one thing, they say the "pension pick-up" is a non-starter.

"If the Board of Education imposes a 7 percent slash in our salaries, we will move to strike," Lewis said at a news conference last month. "Cutting our pay is unacceptable — and for years, the 'pension pickup' as the Board has called it, was part of our compensation package."

"This was not a perk," she added. "This was negotiated compensation with the Board of Education."

By their calculations, union representatives say the current version of the contract would actually cut their take-home pay by about 3 percent over four years. Part of the reason for the discrepancy is that the union, unlike CPS leaders, doesn't consider pay hikes given for advances in "steps" or "lanes" — which are set based on experience or advanced education levels — as a salary increase.

"Over 90 percent of school districts in Illinois recognize [steps and lanes] as part of the experience/level of education ladder in teaching," according to the union's blog. "CPS is trying to alter that permanently and count them as cost of living raises in order to reduce our compensation."

The union also wants rigid limits on class sizes. CPS guidelines say no class should have more than 28 students, but there's no hard rule for what happens when that number is exceeded.

"Fewer employees, including teachers’ aides, means enormous class sizes," Lewis said, referring to teacher layoffs announced over the summer. "The more students in a classroom means fewer minutes of personalized instruction for each student."

How likely is a strike?

It depends on whom you ask. In every public statement since the beginning of the year, CPS representatives and their allies — like Mayor Rahm Emanuel — have expressed optimism that a deal can be reached in time to avoid a walkout.

"CPS remains open and willing to listen to any ideas that [union] leadership presents to make the existing framework better for both parties," according to Bittner's statement. “We are hopeful that a strike can be averted, and we are committed to working at the bargaining table to reach a fair contract."

Union leaders say they're still open to negotiate, too, but Lewis already has started beating the drum for a strike. On Aug. 22, she suggested that most teachers are already eager to start drawing their picket signs.

“Members are so angry that many have said they’re ready to strike now before school is set to open,” Lewis wrote in a message to union members, according to the Sun-Times. “That anger is morally justified, but anger needs to be married with strategy in order to win the best possible outcome."

At last month's press conference, Lewis told parents to "pay close attention to what is going on over the next few weeks so you can be prepared" if a strike is approved.

Teachers should "save as much money as [they] can," she added.

How would a strike this year be different from 2012?

By the time teachers packed up their picket signs after an eight-day strike in 2012, Emanuel had scored a number of concessions, including new accountability measures and a longer school day.

But the political landscape in 2016 is starkly different from the Chicago of four years ago.

Emanuel suffered massive blowback for his decision to permanently close 49 public schools in 2013. And many in the city were calling for his resignation after he was accused of concealing dashcam footage showing the 2014 killing of 17-year-old Laquan McDonald at the hands of a police officer.

In December 2015, an Aldertrack/DNAinfo/WGN Radio poll showed the mayor with a 56 percent disapproval rating.

Union leaders intend to use that unpopularity to their advantage.

“We do not know if Mayor Emanuel can stand another teachers strike, especially at a time when confidence in his leadership is at an all-time low," Lewis said last month, "and when the city is in an uproar over another police shooting of an unarmed African-American youth."

Lewis was referring Paul O'Neal, 18, who was shot to death by a Chicago Police officer on July 28.

“Do not force our hand,” she said.

For more neighborhood news, listen to DNAinfo Radio here: