Republicans in the U.S. Senate have blocked a bill that would have imposed a new minimum tax rate on millionaires, a plan President Barack Obama has pushed as both parties present election-year proposals on taxes and the economy.

The Senate voted 51-45 largely along party lines Monday, with majority Democrats not able to get the 60 votes needed to move the so-called “Buffett Rule” forward.

The measure would have established a minimum tax rate of 30 percent for people who make more than $1 million a year. Many wealthy Americans pay less in taxes because of income earned through investments that is taxed at a lower rate.

Mr. Obama said in a statement following the vote that Republicans have chosen to “protect tax breaks for the wealthiest few Americans at the expense of the middle class.” He called the tax proposal “common sense” and said the United States cannot continue to provide tax breaks to the wealthy at a time of “significant” budget deficits.

Republicans say the plan would not help solve the nation's economic problems, including job creation.

The Republican-led House of Representatives is expected to pass a bill later this week calling for small business tax cuts. It is not likely to pass in the Senate.

The Buffett rule is named after billionaire investor Warren Buffett, who has maintained that wealthy investors should not pay a lower tax rate than middle-class wage earners.