Madison, Wis.—As union supporters geared up for their for sixth day of protests at the Wisconsin Capitol, Gov. Scott Walker reiterated Sunday that he wouldn't compromise on the issue that had mobilized them, a bill that would eliminate most of public employees' collective bargaining rights.

Democratic lawmakers have said they and union members would agree to financial concessions that the Republican governor wants in exchange for workers keeping their collective-bargaining rights. But Mr. Walker said he wasn't willing to budge,...