US President Barack Obama on Saturday urged Congress to pass the so-called "Buffett Rule," which calls for increasing the tax rate on Americans making more than $1 million a year.

"Most Americans support this idea," Obama said in his weekly radio and Internet address. "One survey found that two-thirds of millionaires do, too. So do nearly half of all Republicans."

The "Buffet Rule" was named after billionaire investor Warren Buffett, who has publicly spoken out against being taxed at a lower rate than his secretary -- a consequence of tax loopholes imposed by former president George W. Bush under which investment revenues are taxed at a lower rate than wages.

The bill would keep the tax rates unchanged for those making under $250,000 a year.

The US Senate is scheduled to vote on the "Buffett Rule" on Monday. However the fate of the legislation is uncertain as Republicans, who hold a majority in the House of Representatives, oppose it, arguing that Obama's statements are likely aimed at his political opponent, Mitt Romney, who is a multi-millionaire.

But the president said in his address that the proposal was not just about fairness.