The number of the people in the U.S. who believe their income taxes are fair is the lowest in a dozen years, according to a Gallup poll released Monday.

The poll, released on Tax Day in the U.S., found that 55 percent of people in the U.S. believe their taxes are fair, down 4 percentage points from last year and 9 points from the a recent high in 2003.

Gallup chalked up the decline mostly to Republicans, who are now about evenly split on how fair or unfair their taxes are. About two-thirds of Democrats think their taxes are fair, with the split between the two parties growing since George W. Bush left the White House.

The latest findings from Gallup also come after Washington allowed tax rates for family income above $450,000 a year to rise.