The Chicago Teachers Union may be making moves to speed up contract talks, and to signal a strike. (Source: WGN - Chicago)

The Chicago Teachers Union filed a 10-day strike notice on Wednesday in an attempt to put additional pressure on Chicago Public Schools negotiators in ongoing contract talks.

At a packed news conference Wednesday, CTU president Karen Lewis accused CPS leaders and the mayor of engaging in a "smear campaign" against teachers, raising the possibility for the city's first teachers' strike in 25 years.

"It has been insult after insult after insult. Enough is enough," Lewis said.

By filing the required 10-day notice Wednesday with the CPS school board and the Illinois Educational Labor Relations Board, teachers are eligible to strike beginning on Sept. 10, the start of the second week of school for the majority of CPS students.

The union's House of Delegates will meet Thursday where they will review the district's latest contract offer and likely set a strike date.

"I want to make clear that we will remain at the (negotiating) table until a deal gets done," Lewis said. "We will have a contract and it will come the easy way or the hard way."

Responding to the union’s announcement, CPS chief Jean-Claude Brizard issued a statement Wednesday evening, saying “everyone knows that a strike would only hurt our kids.”

“(Students) can't afford to be removed from the classroom just as they're making progress with the new full school day,” Brizard said. “That's why we'll continue to meet every day until we reach a fair resolution for our teachers and avoid any disruption to our kids' school year. If CTU leadership decides to strike, we will be prepared to provide our students with the services they need to keep them fed and in a safe environment with positive activities.”

Lewis said the two sides have made strides during contract talks on "small issues," such as winning provisions for teachers who are nursing mothers and ensuring text books for students in schools with limited resources.

But, Lewis said, the biggest issues still remain, such as teacher raises and a re-hiring pool for those who've been laid off. Contract talks will continue all this week, and likely through the weekend, Lewis said.

"CPS seems determined to have a toxic relationship with its employees," Lewis said.

The teachers have remained angry with CPS administration even after a deal on the longer school day in which the district agreed to hire 477 teachers who had been laid off. That allowed teachers to work the same number of hours even though students are in school longer.

CPS has budgeted spending as much as $25 million on a strike contingency plan. District spokeswoman Becky Carroll said CPS is intent on providing a “safe and engaging” environment for as many of the district’s 402,000 students as possible.

The plan would likely include opening some schools and perhaps other city buildings so that students can receive breakfast and lunch and play in organized activities. State law prohibits the district from engaging students in traditional classroom instruction without certified teachers, Carroll said.

“If the Chicago Teachers Union chooses to strike, we'll be prepared to serve our kids,” Carroll said. “Students can't afford to be removed from their classroom at a time when they're starting to make progress with the full school day. They belong in school with their teachers, which is why we need to stay at the table and keep negotiating, every day if needed, until we reach a fair resolution as a strike would only hurt our kids."