West Chicago High School teachers voted Friday to authorize a strike but have not set a date for a possible walkout that would raise the stakes in a contract dispute after almost two years at the table.

The vote by 129 members of the West Chicago High School Teachers Association was "without opposition," union President Brad Larson said. Teachers also have agreed to enter into a lease to secure a location for a strike headquarters.

The authorization vote is one of the steps the union must take before teachers legally can walk off the job. The union also must give the district a 10-day notice of its intent to strike.

The strike threat comes two weeks after the union declared an impasse in contract talks that have failed to produce agreement on salaries, health benefits and other key sticking points.

In a statement, Larson said a strike is "the last thing" teachers want. The association represents 194 teachers.

"But we also realize that unless we are able to attract and retain talented staff, our students and our communities will suffer," Larson said.

Nearly 2,100 students could be left out of classes should teachers strike for the first time since 1984. School board President Gary Saake said the district is working with area libraries and park districts to make alternative programming available for students in the event teachers walk picket lines.

The board, Saake said, is willing to return to the table even before the next scheduled session Feb. 7.

"In the view of the board, a strike would serve no purpose toward collaboratively reaching a contractual agreement and comes at an immeasurable cost to the district, students, parents, community and their co-workers," Saake said in a statement.

The impasse filing with the Illinois Educational Labor Relations Board forced the two sides to exchange contract offers. Negotiators still could not broker a deal by a Tuesday deadline, triggering the public posting of both proposals on the state labor board's website.

During a session Monday, the school board presented a new wage offer that would increase salaries for the union members by an average of roughly 12 percent in four years. Saake called it a "very generous offer."

"We see that as very comparable with all our neighboring districts," he said.

Union negotiators said this week they are seeking average salary increases of 17 percent over the course of a four-year contract.

In previous contracts, union leaders say, teachers have made significant concessions. In its report to the state labor board, the union cited an agreement to forgo automatic 2.75 percent annual step increases to teacher salaries for multiple years.

School board negotiators also have expressed deep frustration with the slow pace of talks. The board and the union started preliminary contract discussions in April 2016. The board last April presented a full proposal with a new salary structure based on a conceptual agreement with the union. The union delivered its own proposal two months later.

Teachers have been working under the terms of a one-year contract extension that expired in August.