Gina McCarthy, President Obama’s nominee to replace Lisa Jackson as head of the Environmental Protection Agency, has stonewalled Congress about the clean air rules she has been developing, according to lawmakers who demand access to “secret data” pertaining to the regulations.

“EPA has continually refused to make public the basic scientific data underlying virtually all of the Agency’s claimed benefits from new Clean Air Act (CAA) rules,” Sen. David Vitter, R-La., and Rep. Lamar Smith, R-Texas, wrote in a sharp letter to McCarthy, who oversees the development of CAA regulations.

“You and other high-ranking Administration officials have repeatedly backtracked and reneged on promises to Members of Congress to make the scientific information that underpins the Agency’s basic associations between air quality and mortality available to the public and independent scientists over the last year and a half,” they continued.

Vitter and Smith fired off the letter today as President Obama nominated McCarthy to serve as EPA administrator. “I think there is nobody who can do a better job in filling Lisa’s shoes permanently than my nominee who’s standing beside me here — Gina McCarthy,” Obama said this morning. “As Assistant EPA Administrator, Gina has focused on practical, cost-effective ways to keep our air clean and our economy growing.  She’s earned a reputation as a straight shooter.  She welcomes different points of views.”

The Republicans who oversee the EPA are less confident that McCarthy is a “straight shooter,”  despite Obama’s comment.

“The EPA’s new CAA regulations are expected to be some of the most costly the federal government has ever issued,” Vitter and Smith wrote today.  “Relying on secret data to support these rules is not acceptable.  The public and outside scientists must be able to independently verify the EPA’s claims, especially when the results are contradicted by so many other studies.”

Jackson resigned earlier this year — a common enough move for veterans of a first-term administration. But her resignation also came, incidentally, as Congress and the EPA inspector general were investigating her use of a secret email account to conduct official EPA business under the alias, Richard Windsor.