President Barack Obama called on Congress to require the highest earners to pay at least 30 per cent of their income in taxes, building on his election-year push for what he terms economic fairness.

The President's proposal in his State of the Union address is intended to create a minimum tax on income exceeding $1 million, according to a White House fact sheet. That floor would be established in part by eliminating high earners' deductions for mortgage interest, healthcare, retirement and childcare, the fact sheet said. Given congressional gridlock, there is little chance of its enactment this year.

Mr Obama is pressuring Republicans, who have resisted tax increases, on a day that began with Republican presidential candidate Mitt Romney releasing tax returns showing he paid a 13.9 per cent tax rate in 2010 on $21.6 million in income.

"We can either settle for a country where a shrinking number of people do really well, while a growing number of Americans barely get by," Mr Obama said in his address to a joint session of Congress.