HIGHLAND PARK, Ill. (CBS) — Teachers in a third local school district could go on strike next month, joining their counterparts in Chicago and Lake Forest in staging a walkout amid stalled contract talks.

The teachers’ union in North Shore School District 112 in Highland Park has declared an impasse in contract talks, setting the stage for a possible strike next month.

A union spokesman said Friday the School Board is proposing to freeze teachers’ pay for two years and link a third-year raise to the Consumer Price Index.

Other outstanding issues include the pay raises teachers receive for completing coursework and pre-retirement pay incentives.

“The board’s current proposal will result in District 112 being one of the worst school districts on the North Shore in terms of teachers’ benefits,” said Pamela Kramer, president of the North Shore Education Association.

“That will cause teachers to use their time in District 112 as a stepping stone to other better-paying districts where teachers are respected and receive better benefits. We do not want District 112 to become a revolving door.”

Average teacher pay in the district was reported at $70,566 on the 2011 School Report Cards, based on an average experience level of 11.5 years. The district serves 4,300 pupils in Highland Park and Highwood.

Under the contract that expired Aug. 21, a starting teacher with a bachelor’s degree earned $41,149, while the maximum pay was $107,345 for a 22-year veteran with a master’s degree, plus 45 additional course hours.

The North Shore Education Association notified the School Board on Friday that it was declaring an impasse in negotiations and filing the motion with the Illinois Educational Labor Relations Board.

Kramer said that prior to negotiations, the union agreed to changes in health insurance coverage estimated to save the district about $486,000 a year, or nearly $1.5 million over the three-year contract period. The changes included higher deductibles and co-pays.

Andi Rosen, the district’s community relations specialist, expressed surprise at the impasse move Friday, noting that another mediation session is set for Oct. 4.

The union and School Board have seven days, or until Sept. 21, to submit their “last, best offers” to the state agency and detail the costs associated with their proposals.

The labor board has another seven days to post the proposals on the agency’s Web site.

The impasse was declared after a third negotiating session with a federal mediator on Wednesday, Sept. 12.

In a Sept. 5 vote, teachers authorized their negotiating team to call a strike if talks failed to produce an acceptable agreement.

By law, teachers must provide the School Board with notice of their intent to strike at least 10 days prior to a work stoppage. That has not occurred.

The Sun-Times Media Wire contributed to this report.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2012. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)