Rep. Henry Waxman, D-Calif., wants to question key U.S. Environmental Protection officials as to why the federal agency blocked California's request to regulate tailpipe emission.

Waxman, the chair of the House Oversight and Government Reform Committee, sent a letter Monday to EPA Administrator Stephen Johnson stating he wants to interview or depose seven high-level staff members.

The list of officials Waxman wants to talk to include Margo Oge, director of transportation and air quality; Brian McLean, director of atmospheric programs; and Rob Brenner, director of program analysis and review.

Under the Federal Clean Air Act, California has the right to set its own vehicle-emissions standards as long as it obtains a waiver from the EPA.

In December, the EPA rejected the state's request for a waiver, explaining that the country's energy bill that was signed into law by President Bush was good enough and prevented states from creating a confusing patchwork of rules.

California's emissions law, which passed in 2002, requires a 30-percent reduction in greenhouse-gas emissions from vehicles by 2016 (see EPA Rejects California Vehicle-Emission Standards).

Sixteen other states also have adopted or are considering adopting California's emission standards.

In response to the rejection, Waxman sent an angry letter to the EPA in December, accusing the agency of overruling unanimous recommendations of its legal and technical staffs in denying California's petition.

He then asked the agency to hand over all documents, including e-mails and other communications to the White House, related to the decision.

And it appears, at least from Waxman's latest letter, that he hasn't received much of a response.

Waxman also asked the EPA to tell his committee by Wednesday when the documents will be available.

EPA spokesman Jonathan Shradar said the agency would work with Waxman's committee to schedule meetings and is working on gathering the documents, according to the Associated Press.

Over the past 30 years, the EPA has granted more than 40 such waivers while denying none, according to California Gov. Arnold Schwarzenegger.

Earlier this month, California Attorney General Jerry Brown sued the EPA over the issue (see Emissions Technologies Could Benefit From Regulation Battle).

California and the EPA have faced off since 2005, when the state first asked for the waiver.