Portland teachers say they are "shocked" at the decision by Portland Public Schools to declare an impasse Wednesday.
The two sides have been in mediation for more than a month. The declaration of impasse requires both sides to submit final offers within seven days.
The district says "impasse" helped the two sides reach a deal three years ago, and could have the same result this time.
Portland Association of Teachers president, Gwen Sullivan, says it's not a positive step.
"This brought us, I would say, to a much more dangerous place -- moving our city and our schools that much closer to a potential strike," according to Sullivan.
Sullivan says the likelihood of a strike depends on what the district proposes in upcoming bargaining sessions.
The district says the union's proposals on class size and teacher workloads would add more than $200 million to the budget.
Union leaders say their proposal is a response to the district's effort to remove workload limits that were in the contract that expired last June.
Significant differences remain around health insurance, salary, and rules for transferring teachers.
This story originally appeared on Oregon Public Broadcasting.