Sen. Bob Corker on Wednesday threatened to vote against an increase in the country's borrowing limit unless government spending reductions are included.
The Tennessee Republican told CNBC spending must be reduced to 20.6 percent of gross domestic product, which he characterized as a historic average.
"I have found that it's irresponsible not to be responsible prior to a debt ceiling increase," said Corker. "If we don't have something that dramatically changes spending in this country and gets it in line, I will not vote for a debt ceiling increase."
He disagreed with Treasury Secretary Tim Geithner that there are "minor differences" between the Obama administration and congressional Republicans on solving the rising debt problem.
"The fact is we don’t need to have deficit spending targets, we need to have spending relative to our GDP targets. This is an important difference," he said. "I hope he will act more like the Secretary of the Treasury for the United States and less as a staffer to the administration."
Geithner spoke on CNBC Tuesday after Standard & Poor's said it was downgrading its outlook on the United States to negative from stable, in part because of the disagreement between Republicans and the administration.
While affirming the US's AAA rating, S&P said a downgrade is possible if Congress and the Obama administration fail to enact a credible deficit reduction plan.
Corker said he wants to "prove S&P wrong," even as he criticized Geithner.