Chicago teachers begin vote to authorize strike next month

CHICAGO - Chicago teachers are voting on whether to authorize a strike next month as contract negotiations continue in the nation's third-largest school district. 

Voting members of the Chicago Teachers Union start casting ballots Tuesday. Democratic presidential candidate Bernie Sanders is expected to join a teacher rally Tuesday evening. 

The voting will continue until at least Thursday. To strike, 75% must vote in favor. The earliest a strike could take place is Oct. 7. 

Educators and Chicago Public Schools officials have been negotiating pay and staffing shortages, among other issues. 

Union members say they remain far apart. District officials say their latest offer is strong. 

CTU wants a 15% raise over a three-year contract. The district's latest offer is a 16% total raise over a five-year contract.