PORTLAND, Ore. (AP) — Teachers in Portland, Oregon, temporarily shut down a major bridge Tuesday morning as they marched in a strike started roughly three weeks ago.

Members of the Portland Association of Teachers union and their supporters stopped in the middle of the Burnside Bridge for about 15 minutes, KGW reported. By 9 a.m. the bridge was clear and cars were driving across, according to the news outlet.

Photos posted by the union on its Facebook page showed teachers sitting down on the bridge donning blue clothes and holding banners calling for better pay and teaching conditions. The union had called on supporters to meet at its headquarters, roughly half a mile from the bridge, at 7:30 a.m. before beginning the march at 8 a.m.

Portland teachers have been on strike since Nov. 1, shuttering schools serving about 45,000 students in Oregon’s largest district. Students have missed 11 days of class because of the walkout.

In marathon bargaining sessions that at times went through the night, the teachers union and the district have negotiated pay, class sizes and planning time for teachers.

The union initially proposed caps on class sizes, but amid pushback from the district on how much that would cost, it is now asking instead for increased pay for teachers whose class sizes surpass certain thresholds.

In recent days, questions over parent involvement in proposed committees to oversee class sizes have become a major sticking point.

The union has proposed allowing parents to be a part of committees that would decide whether students could be added to a class that has already met the size threshold. The district said this would violate students’ privacy and that such decisions should be handled by teachers, principals and school administrators.

On Monday morning, the union said school board members had rejected a tentative agreement. In a news conference, board members disputed the claim but said they felt a deal was “very, very close.”

The two sides appear to have made some progress on salary negotiations. In its latest proposal on Monday, the district proposed cost-of-living adjustments that would increase teacher salaries by roughly 13% over three years, bringing it closer to the roughly 20% pay increase over three years that the union had initially asked for.