Last week, I reported that the Congressional Budget Office was updating some of its cost estimates of the national health care law as part of its regular budget review process. But today, 37 Senators led by freshman Sen. Ron Johnson, R-Wis., sent a letter to CBO director Doug Elmendorf asking for a re-estimate of the entire law in light of new information.

Several factors could make the health care law significantly more costly than advertised at the time of passage in March 2010. For instance, the law was crafted in a way to delay enactment of the major spending provisions until 2014, to make the legislation appear cheaper under the CBO’s 10-year budget window (then 2010 to 2019).  Now, the budget window has moved up to 2022, meaning it takes into account an extra three years of full enactment.

Also, unemployment forecasts are worse now than at the time the law passed, which affects projections for how many people will rely on Medicaid qualify for insurance subsidies.

Johnson has focused on another area, citing data suggesting that far more employers would dump employers on to the government exchanges that originally projected.

"To be able to claim that his health care plan would not increase the debt, the President and his allies in Congress engineered an unrealistic low-ball estimate of the cost of Obamacare," Johnson said in a statement. "A key part of that fiction is an unrealistically low estimate of how many Americans will be dumped into the health insurance exchanges. The fact is that many millions more Americans will be put into this exchange costing hundreds of billions – possibly trillions of dollars more – if ObamaCare is not repealed.  CBO owes the American public realistic estimate of the true cost of ObamaCare.”

Click here to read the letter, and view all the other co-signers.