Obama was ready to quickly strike back with a White House event where he was certain to hammer Republicans and again argue that 16 million minimum-wage workers deserve a raise.
Senate Republicans appeared to have more than enough votes to sustain a procedural roadblock known as a filibuster against the bill, which would hike the minimum wage, now at $7.25 per hour, to $10.10 per hour during the next three years and then adjust it in the future for inflation.
Democrats control the Senate, 55-45, but need 60 votes to end the filibuster and begin consideration of the measure.
The Senate vote was expected in the early afternoon with Obama scheduled to speak from the White House about three hours later.
The non-partisan Congressional Budget Office estimated that the bill would lift raise the wages of about 16.5 million Americans and lift 900,000 out of poverty. But it also estimated the bill could cost up to 1 million Americans their jobs because businesses may simply be unable to afford to pay them.
Polls show that most Americans, upward of 60 percent, say they would support an increase in the minimum wage.
(Reporting By Thomas Ferraro; Editing by Jim Loney)