Voters in Arkansas and Missouri approved an increase to their state minimum wages over the next few years, while other labor-backed ballot initiatives had mixed results.

Issue 5 in Arkansas was approved Nov. 6 by a margin of 68 percent to 31 percent, according to state voting results. Proposition B in Missouri got the OK by 62 percent to 37 percent.

Arkansas’ measure will increase the current hourly wage floor from $8.50 to $11 by 2021. The wages will increase...