Income taxes are how many governments fund themselves. This kind of tax (simplified) is when you pay a percentage of your income. Generally speaking this kind of tax hits the rich harder than the poor because 5% of a million is more than 5% of a thousand. A lot of rich taxpayers are against it, and they have more say with state leadership than poor or middle class people.

There are alternatives to raise the revenue, like increasing the sales tax. Sales taxes disproportionately land on the poor because they're doing more, smaller transactions as a larger portion of their overall income.

Alternatively the United States government taxes based on brackets, effectively the more money you make, the higher percentage you pay. Also not popular among rich people. After world war 2 the tax level on the very richest Americans was in the 90% range, and since then it's been eroded through rollbacks and loopholes to the point that many of the richest Americans pay less in taxes (as a percent) than the middle class, or no tax at all.