Some 25,000 Chicago teachers Monday were poised to walk off the job at midnight as negotiators for the Board of Education and the Chicago Teachers Union engaged in an intense round of talks.

A strike would affect about 300,000 schoolchildren.

Union members picked up strike materials and were told to be ready to picket at 6 a.m. Tuesday.

A Chicago Public Schools official told the Chicago Tribune the two sides are “not too far apart on the economics,” but it was unclear whether enough progress had been made to stave off a strike.

Among the issues holding up a contract is whether teachers will have to pick up more of the contribution to their pension fund. The CTU has opposed any increase, saying the district agreed to pick up the 7 percent tab in exchange for smaller raises in previous agreements.

The union is pushing for “job security, no cuts to pay and benefits, adequate staffing levels, resources for students” and more revenue for schools.

Chicago teachers earn less than their suburban counterparts. The average salary in Chicago was $69,000 in 2015, compared to suburban districts that pay $80,000 to $100,000.

Complicating the matter is a 3.5 percent drop in enrollment from last year, a loss of 13,000 students. Nearly 500 teachers were laid off before the school year began, more than half of whom had tenure.

Any proposal would need approval from the 40-member union bargaining team before it could be submitted to the rank-and-file.

Negotiations began at noon and were scheduled to stretch late into the evening.

Mayor Rahm Emanuel said Monday the tone of the talks is positive in sharp contrast to previous rounds.

Hundreds of teachers picked up signs and T-shirts at CTU headquarters Monday afternoon as they expressed hope the materials wouldn’t be needed. The union posted a list of chants for picketers on its blog.

Among the more pointed:

Hey, fat cats,

We're NO FOOLS!

You ROB your workers and

STEAL from schools.

And

We pay taxes,

WHY DON’T THEY?

Bankers and Billionaires

Ought to PAY.

"You don't do all of this unless it is serious," teacher Ed Hershey told DNAinfo Chicago from strike headquarters Monday.

Earlier in the day, demonstrators protested near Emanuel’s North Side home to try to pressure the city to free up tax-increment financing for schools. The city already has ponied up $32 million in surplus funds.

The teachers contract expired in June 2015.

A contract proposal reached by top negotiators last January was nixed by the bargaining team, which was scheduled to join the talks later in the evening.

The union has asked for $200 million — $500 more per pupil — “to stabilize schools and strengthen classrooms,” the Chicago Sun-Times reported, noting classroom conditions are not a strikeable issue. The teachers also are looking for no pay cuts.

School officials plan to keep buildings open to serve breakfast and lunch to children who show up. The board budgeted $15 million to keep schools open during a strike. No classes or after-school sports will be scheduled.