State income taxes are structured in many different ways, and many of them have tax brackets of their own that apply to people of various income levels. One interesting phenomenon involves what many call the millionaire tax.

In some states, the millionaire tax takes the form of the government imposing a higher tax bracket on those making $1 million or more in income. Others don't hang as much on the $1 million mark, but the rest of their brackets make it clear that the levy is aimed at those who are relatively rich within the state's borders. Below, we'll go through the jurisdictions that already have millionaire taxes, and then look to see if the list could get longer in the near future.

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1. California

The state of California has a whopping 10 different tax brackets, starting 1% on the first $8,015 of income for single filers. However, the top 13.3% tax bracket takes effect for singles earning $1 million or more.

As millionaire taxes go, California's is pretty benign, in that it only adds a single percentage point to the rate that's immediately below it. However, when you consider that the rate that applies between about $52,000 and $268,000 for single filers is 9.3%, the 4-percentage-point increase for what the state characterizes as high-income earners looks a little more like a true millionaire tax.

2. Connecticut

Connecticut is even sillier in its imposition of a millionaire tax. The top rate of 6.99% applies to joint filers with income of $1 million or more. However, that's less than a 10th of a percentage point above the 6.9% rate that applies for those with income between $500,000 and $1 million.

Connecticut has the second-highest concentration of millionaires in the U.S., ranking only behind Maryland on a per-capita basis. However, like many Northeastern states, Connecticut has seen some of its wealthier population move to low- or no-tax states like Florida, causing declines in total tax revenue.

3. Maine

Maine doesn't have a millionaire tax by pure definition, but it does have a substantially higher rate that starts well above the second-highest bracket. For those making more than $200,000, the rate goes from 7.15% to 10.15%.

Maine added the new tax rate in the 2016 elections, which gave Maine the second-highest top tax bracket in the nation second only to California. The measure passed by the barest of margins, 50.4% to 49.5%, but an initially requested recount was abandoned.

4. New Jersey

In New Jersey, the 8.97% rate kicks in for those making $500,000 or more, whether filing singly or jointly. The rate is 2.6 percentage points higher than what applies to the next-lower bracket, which extends downward to $75,000 for singles and $150,000 for joint filers.

More recently, though, lawmakers have looked at adding another surcharge at $1 million. The move would aim to fund New Jersey public pensions, which suffer from underfunding.

5. New York

New York has a true millionaire tax, with the 8.82% rate that applies to singles with taxable income of $1,077,500. Joint filers with income of $2,155,350 also pay the higher rate, which is almost 2 percentage points more in tax than the next higher bracket.

New York's millionaire tax, enacted in 2009, was initially designed to be temporary. However, the measure has already been renewed before, and New York Governor Andrew Cuomo has again called for an extension beyond 2017.

6. Washington, D.C.

Obviously, the District of Columbia isn't a state, but it does have a local income tax that includes millionaire provisions. For those with incomes of more than $1 million, the tax rate gets a 0.2 percentage point boost to 8.95%.

Will more states add a millionaire tax?

It's possible that this list will get longer in the near future. Voters in Massachusetts could vote as soon as 2018 on a measure to add a millionaire tax, which would mark the first departure from the current flat-tax scheme that imposes a single rate on taxpayers of all income levels. The proposal will be structured as a constitutional amendment, taking the decision out of lawmakers' hands. Opponents argue that the increase from 5.1% to 9.1% for those with incomes above $1 million will drive high-income taxpayers out of the state, while proponents argue that stories of tax flight have been anecdotal and lack large numbers to back them up.

Millionaire taxes have grown in popularity as more people call for higher levies on the rich to combat income inequality. If popular discontent continues, then the list of states with millionaire taxes is likely to get bigger over the long haul.

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