WASHINGTON (AP) - President Barack Obama is urging Congress to boost taxes on millionaires, traveling to Florida to make a populist pitch about economic fairness.

Obama is outlining his support for the so-called Buffett rule at Florida Atlantic University in Boca Raton, arguing that wealthy investors shouldn't pay taxes at a lower rate than middle-class earners.

Obama's campaign views the proposal in stark contrast to Republican front-runner Mitt Romney, whose campaign says it would lead to raising taxes on small businesses.

The push for the Buffett rule, named after billionaire investor Warren Buffett, comes as millions of Americans prepare to file their taxes. The plan has little chance of passing Congress but Senate Democrats are pushing for a vote next week.

Obama is also holding three fundraisers as part of his Florida trip.