House Republicans are tired of waiting for the White House to disclose how many Obamacare enrollees have paid their premiums—so they're asking the insurers themselves.
If insurer data match anecdotal reports nationwide, the Affordable Care Act's enrollment tally will fall significantly short of the 6 million person goal the White House is hoping to hit by the end of this month.
The House Energy and Commerce Committee on Thursday wrote every insurance company participating in the federal Obamacare exchange asking for "specific enrollment data, including the first month's premium and those who are identified as previously uninsured," the GOP-controlled committee said in a press release.
The House committee's request was not made to insurers who are only selling Obamacare plans on one of the 15 exchanges being run by individual states and the District of Columbia.
(Read more: Insurers scope out Obamacare enrollees)
"Who's paid? That's what Congress wants to know as the Obama administration refuses to be straight with the American public," said Rep. Fred Upton, R-Mich. "In the wake of the law's troubled rollout, officials have tried for months to backtrack and redefine metrics for success."
"If the administration won't provide transparency, we will work with every insurance provider to get the real picture the White House seemingly wants to hide from the public."
The Obama administration on Tuesday revealed that 4.2 million people had enrolled in private insurance plans sold on government-run exchanges by the end of February.
But for more than a month, a series of reports have suggested that the actual enrollment rate is 15 to 20 percent less than reported sign-ups. That's because some people have not paid for their first months' premiums after selecting a plan, which is required for official enrollment.
During the release of Tuesday's data, administration officials repeatedly said they did not know the rate of people who have not paid, nor did they know how many enrollees were previously uninsured. They maintained their stance even in the face of repeated questioning by reporters, who asked them if there wasn't some way to find out those statistics now, instead of waiting until after the close of open enrollment on March 31.
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When asked how many people have while testifying before the House on Wednesday, Health and Human Services Secretary Kathleen Sebelius said, "I can't tell you because I don't know." She ducked a question on whether the administration has asked insurers for that data.
A White House spokesman had earlier said that "questions about who exactly has paid for the health insurance can best be directed to those private insurance companies that are collecting the payments."
In a response to the House committee's move, a spokesman for the Centers for Medicare & Medicaid Services, which operates HealthCare.gov, said in an email Thursday, "We are focused on providing reliable and accurate information and right now, we do not have full, complete, accurate data on individuals who have paid their plans." He added that the organization will later "determine the most appropriate way" to report the number of enrollees who have paid their premiums.
The dispute about the actual enrollment tally reflects how proponents and opponents of Obamacare are relying on numbers to justify their arguments that the health-care reform law is either working or failing.
Obama administration officials had originally projected that by March 31, a total of 7 million people would enroll in ACA plans sold on HealthCare.gov and the 15 other Obamacare exchanges being operated by individual states and the District of Columbia.
Officials recently revised that estimate down to 6 million, reflecting the fact that the first two months of open enrollment were a disaster because of technological problems on the federal exchange, and a number of state-run marketplaces.
The consulting company Avalere Health this week estimated that enrollment by the March 31 deadline would fall short of even the new estimate, saying it expected about 5.5 million would enroll.
But even that prediction reflects the reported enrollment by the government exchanges, not the actual number of people who have paid for their first month of premiums.
(Read more: Obamacare: ACA enrollment just 4.2 million by Feb)
Assuming the most conservative estimate that 15 percent of enrollees don't end up making such payments, that would mean less than 4.7 million people would be enrolled by the end of this month.
That low number would give fodder to Obamacare critics, particularly if a large percentage of the enrollees turn out to be people who lost their prior health insurance plans because they weren't compliant with ACA standards, as opposed to the previously uninsured who are the main targets of the health-care reform effort.
Bobby Koritala, chief product officer of the insurance data integrity provider Infogix, said it's likely that the Obama administration doesn't actually know how many members have paid their premiums because of the fact that "there is no ongoing reporting requirement where the plans need to report member premium payments to the government."
"The only indirect way for the government to find out would be if members fail to pay their premiums and the plans cancel their coverage. This would result in the dropping of the premium subsidy from the government as well, hence they would know that the enrollment dropped—but not necessarily why," he said.
The subsidies Koritala was referring to are the tax credits from the federal government, which are available to many low- or moderate-income Obamacare enrollees.
He also said insurers are seeing that "some kinds of enrollees are paying upfront, and some are not."
"People who previously had insurance are in the habit of paying," and have been making their first payments at a higher rate than the average, Koritala said.
"The ones who have never had insurance? They're the ones that are having trouble," he said. "They're not used to paying an insurance premium."
—By CNBC's Dan Mangan. Follow him on Twitter @_DanMangan