At some point in the latest round of talks with the Portland Public Schools (PPS) last Friday, teachers union officials became convinced a strike might be necessary.

"They began to say things like 'We don't have any more ideas,'" Portland Association of Teachers (PAT) President Gwen Sullivan said this morning in a sit down with reporters. "We began to see kind of a slow play from the district."

So after a vote union members described as nearly unanimous last night, the PAT has formally filed notice today with the Oregon Employment Relations Board: Absent an agreement, teachers will walk February 20th—the first-such strike in the district's history.

The move contrasts with the union's tenor a couple weeks back, as PAT representatives met with teachers individually to get a sense of how much support there was for a strike. Sullivan at the time said it was merely a precaution in case PPS chose to impose labor conditions.

"Our hope is still not to go on strike," she said this morning. " The district has the power and authority to figure this out right now."

Chief among the union's concerns: Teacher workloads. The PAT has said the school district—relatively flush with cash this year—should hire 175 new teachers. PPS has offered 88 new hires, and says it's open to adding more as part of the budget process.

The union has also cited benefits, pay, hiring policies and the question of whether student performance should affect teacher evaluations, among other sticking points.

"I think what you're looking at is misplaced priorities by the district leadership," Bill Wilson, chair of the negotiating team and a science teacher at Grant High School. "Teachers are tired."

The union and PPS have a mediation session scheduled on Sunday, and PAT officials have repeatedly said they'd like to meet before then.

If an arrangement isn't reached two weeks from today, there are big questions about what a strike means for PPS. The district has not shared how it plans to cope with a strike, though it's apparently been recruiting among its substitute teacher rolls. The union, meanwhile, has asked parents to keep their kids home if there's a walkout.

"I don't think it's the best place for students if teachers aren't there," Sullivan said. "This is historical. This is a time when kids need to know that their situation is being compromised."

PPS issued a statement shortly after last night's vote calling the strike announcement "disappointing," and saying a walkout would be "very disruptive for students and families." A district spokesperson hasn't returned a message for comment this morning.

Since the two groups are at an impasse, the district is free to impose the conditions of its "best final offer" on union members until a formal agreement is reached. That would require a vote by the school board.