On November 8, voters in four states -- Arizona, Colorado, Maine and Washington -- will vote on ballot initiatives calling for a higher minimum wage.

None are calling for $15 an hour, the Holy Grail of many minimum wage campaigns these days.

But the four initiatives are aiming to raise their state's base hourly pay by between 43% and 60%. The increases would be phased in gradually over a few years, and recent polls show a slim majority of support for the wage hikes.

If approved, Washington's current $9.47 minimum wage would rise to $13.50 by 2020. One of its major cities -- Seattle -- has already approved a $15 minimum wage.

The other three states are calling for an increase to $12 by 2020 -- from $8.31 in Colorado, $8.05 in Arizona, and $7.50 in Maine currently.

In all four states, the minimum wage would adjust for cost of living after 2020. Maine's ballot initiative would also raise the state's subminimum wage for tipped workers. And the measures in Arizona and Washington would provide for a minimum of paid sick leave.

Typically minimum wage measures do well on ballots. Since 2000, 15 states have had a higher minimum wage on the ballot and all of them passed, according to the nonpartisan Initiative and Referendum Institute.

If all four ballot initiatives are approved, they could directly benefit roughly 2.1 million workers, according to The Fairness Project, which partners with minimum wage campaigns across the country.

As of this week, Arizona and the 2nd district in Maine are battleground areas, while Colorado leans Democratic and Washington is considered solidly Democratic.

Democrats have been more vocal in pushing the issue of higher minimum wages, but the approval of hikes at the state level hasn't always run along party lines.

During the 2014 mid-term elections, for instance, four red-leaning states -- Alaska, Arkansas, Nebraska and South Dakota -- all approved minimum wage increases.

Where the "Fight for $15" stands

To date only two states (California and New York) and Washington, D.C., have approved a gradual move toward $15. But they're not likely to be the last.

Connecticut has introduced a bill calling for a $15 minimum wage. A similar bill was vetoed in New Jersey, but the proposed hike will appear on a ballot initiative in 2017.

The idea behind ballot initiatives is to give the public a say. "They let voters take actions when their politicians have failed," said Jonathan Schleifer, executive director of The Fairness Project.

Meanwhile, Massachusetts has approved a $15 hourly minimum for home care workers. And there's a campaign there to extend the same wage to fast food and retail workers, according to the National Employment Law Project, another advocacy group.

Among cities, 15 already have approved a move toward a $15 minimum, although the vast majority are in California. Another 6 cities have introduced legislation calling for it -- including Minneapolis; Flagstaff, Arizona; Baltimore and Cleveland.

And a number of other cities have approved a $15 minimum wage for public sector workers and contractors.

Business lobbies that typically oppose big hikes in the minimum wage -- such as the Employment Policies Institute -- contend that they will cause businesses to raise prices, hire fewer people or in some circumstances close down. But it's still too early to definitively gauge the economic effect on the cities and states that have approved large, gradual wage hikes since 2014.

- CNN's Robert Yoon contributed to this report