Which of these forms of taxation has been criticized for placing an excessive burden on people with less ability to pay?

Regressive taxation has one of the most criticised forms of taxation due to its burden on people who are less fortunate to pay. By definition, a regressive tax is " a tax imposed in such a manner that the tax rate decreases as the amount subject to taxation increases" as defined by Wikipedia. It is directly proportionate to the income that the person earns.