The Chicago Teachers Union (CTU) House of Delegates approved a strike authorization vote Wednesday.

The vote is scheduled to begin September 21 and will run through at least September 23. The union's members voted to authorize a strike in the spring, but CTU leaders say a second vote would allow them to ensure the legality of holding a strike this fall.

Chicago public school teachers saw their contracts expire in June 2015 and have been in talks with the district over the terms of a new deal.

The school district and union have been at odds over a cost-of-living increase, benefits and pensions.