WASHINGTON - Both the White House and Republicans in Capitol Hill moved quickly on Tuesday to respond to a nonpartisan report that predicts the healthcare law could cause more job losses in coming years and lowers its estimates of the first-year enrollment of healthcare coverage under the law.

The Affordable Care Act (ACA), commonly known as Obamacare, may cause more Americans to work few hours, drop out of the workforce or delay returning to work, which will cost the United States the equivalent of 2.3 million full-time positions by 2021, according to the latest report by the Congressional Budget Office (CBO).

This is much higher than the nonpartisan agency's previous estimates that the healthcare law will cost the nation the equivalent of 800,000 fewer jobs by 2021.

The nonpartisan agency's latest report found the healthcare law 's negative effects on the economy will be "substantially larger" than its previous estimates.

The report puts the White House and Democrats in Capitol Hill in a more awkward position as the administration has already been under fire for months following the disastrous roll-out of Obamacare websites.

The CBO's report does not actually say that the Obamacare will force employers to fire millions of workers, but instead noted that the healthcare law will increase disincentives for Americans to work and thus in turn will hurt labor supply and economy.

The report found that the largest effects on the work force would not start until 2016 and would be felt the most among lower- wage workers.

Republicans wasted no time to seize on the report and criticize the Obamacare as a "job-killer."

"The middle class is getting squeezed in this economy, and this CBO report confirms that Obamacare is making it worse," said House Speaker John Boehner in a statement.

"Washington can't continue to ignore the problem: trillions of dollars in empty promises. And Obamacare is only making things worse," said Republican congressman Paul Ryan, chairman of the House Budget Committee.

The White House rushed to defend the law that has bedeviled President Barack Obama for years and rebut the Republicans' claims.

"Claims that the Affordable Care Act hurts jobs are simply belied by the facts in the CBO report. CBO's findings are not driven by an assumption that ACA will lead employers to eliminate jobs or reduce hours, in fact, the report itself says that there is no compelling evidence that part-time employment has increased as a result of the ACA," said White House spokesman Jay Carney in a lengthy statement.

Carney also stressed that the CBO report itself confirmed its analysis of the implications of the healthcare law on the labor force is "incomplete."

He argued that the report has failed to take into account the law's slowing of healthcare costs, which will cause the economy to add as many as 400,000 new jobs per year by the end of the decade.

The report also predicted that 6 million Americans will sign up for insurance through the Obamacare's insurance exchanges before a March 31 deadline for coverage in 2014. The number is about 1 million people fewer than the agency's previous estimates due to " significant technical problems encountered in the initial phases" of implementing the Obamacare, said the report.

The Obama administration announced late last month that about 3 million Americans had already signed up for health plans through the federal-run and state-run insurance exchanges under the Obamacare.