Teachers in Portland, Oregon, went on strike Wednesday, shuttering school for some 45,000 students in Oregon's biggest city. The Portland Association of Teachers union said it was the first-ever teacher's strike in the district. Large class sizes, salaries that haven't kept up with inflation and a lack of resources were among the main issues cited by teachers. Schools are closed and there is no classroom or online instruction during the strike. The teacher's union has been bargaining with the school district for months for a new contract after its previous one expired in June. Portland Public Schools did not immediately respond to requests for comment.