President Obama’s proposal to impose a minimum tax rate on those who earn more than $1 million a year was met with derision Sunday by Republican lawmakers, who said it amounted to “class warfare” and a political tactic intended to portray his opponents as indifferent to the hardships facing middle-class Americans.

The tax proposal, which would be introduced in 2013 and limit the deductions and credits that high earners could take once they hit the million-dollar threshold, is part of a broad plan for $2 trillion in deficit reductions that Mr. Obama is expected to unveil on Monday at the White House.