More than 100 unionized musicians with the Chicago Symphony Orchestra are hoisting picket signs instead of violins, clarinets, and French horns after talks aimed at a new contract collapsed March 10.

The Chicago Federation of Musicians said 11 months of negotiations left its members with no choice but to strike. Labor and management remain divided over wages, health benefits, and cuts to the sabbatical program.

The major stumbling block, however, involves the Chicago Symphony Orchestra Association’s demand for changes to the musicians’ retirement scheme. The association hopes to freeze the defined benefit pension plan and shift orchestra members into a...