Voters in four red states approved ballot initiatives to raise their state minimum wages on Tuesday, sending another message to Washington that Americans support a higher wage floor.

Binding minimum wage referendums were on the ballot in Arkansas, Nebraska, Alaska and South Dakota on Tuesday, with polls suggesting ahead of election day that all would pass.

Arkansas voters approved their initiative by a 65-to-35 margin , according to early returns. The measure will increase the minimum wage incrementally to $8.50 per hour by 2017. Nebraska voters, meanwhile, approved their initiative, which will raise the minimum wage to $9 by 2016, by a 62-to-38 margin.

Alaskans voted by a 69-to-31 margin to raise their minimum wage from $7.75 to $9.75 an hour by 2016, and then peg it to an inflation index so that it rises with the cost of living. South Dakota voted 55-45 to raise their minimum wage from $7.25 to $8.50 next year. It will also be indexed thereafter.

The federal minimum wage is just $7.25 per hour and hasn't been raised since 2009, though states have the option of setting their own minimum wages instead. Arkansas and Nebraska will now join 24 other states that are slated to have a higher wage floor than the federal level next year.

Raising the minimum wage is extremely popular among Americans, with 70 percent of respondents to a recent poll saying they back the idea. That support tends to cross party lines, even if Democrats are more enthusiastic about the idea than Republicans .

Supporting minimum wage increases became so fashionable during this midterm election season that even some Republican candidates got behind the ballot initiatives. After discouraging such a raise earlier this year, Dan Sullivan, the Republican challenger to Sen. Mark Begich (D-Alaska), eventually said that he would vote in favor of the Alaska measure. Rep. Tom Cotton (R-Ark.), who unseated Sen. Mark Pryor (D-Ark.) on Tuesday, slowly came around to say he would do the same for the initiative in Arkansas.

Given the broad public support, progressive and labor groups in recent years have made a point of putting minimum wage referendums on the ballot at the state and city level. By going to the ballot box, minimum wage backers are able to bypass reluctant state legislatures, particularly those led by Republicans, and put the vote to what is often a more sympathetic audience.

Recent polls in Arkansas, Alaska and South Dakota all showed support for the minimum wage ballot measures, even though the legislatures in those states are GOP-controlled. Nebraska, though solidly red, does not formally recognize state lawmakers' party affiliation.

Minimum wage increases have been a bright spot for organized labor recently, as unions -- and the Service Employees International Union in particular -- have spearheaded the campaign to raise wages in fast food and retail. Low-wage worker strikes have gained national attention.

President Barack Obama has cited the fast-food strikes in calling on Congress to hike the federal minimum wage. Democrats in both chambers have proposed raising the wage to $10.10 per hour and tying it to an inflation index. House Republicans, however, haven't brought the measure up for a vote, and Senate Democrats haven't rounded up enough votes to overcome a GOP filibuster.

This story was updated after wage increases passed in Alaska and South Dakota.