WASHINGTON — U.S. Sen. David Vitter, R-La., is leading an effort to grill the nominee to lead the federal Environmental Protection Agency over his concerns that her policies may represent the “icing on the cake” in greater regulation of the oil-and-gas industry.

Vitter is citing an uncovered email from the former regional EPA administrator who oversaw Louisiana, Texas and three other states as evidence. Vitter and four other Republican senators on Tuesday sent a letter to the EPA administrator nominee, Gina McCarthy, who currently heads the EPA’s air and radiation office, to demand answers.

The email in question is from EPA Region 6 Administrator Al Armendariz, who resigned in April in the wake of public comments he made surfacing in which he insinuated the need to “crucify” lawbreaking oil and gas companies to set examples.

In the March 30 email to a coworker, Armendariz touted new disclosure requirements for domestic natural gas development, new state rules for such development and additional resources to conduct air emissions inspections.

“None of this would [have] happened had the 2008 election gone the other way. None,” Armendariz wrote in the email.

“We have set things in motion, including empowering and shaming the states, to clean up the oil/gas sector,” he continued. “Further progress is inevitable. I am extremely proud of the work that we have done collectively. Gina’s new air rules will soon be the icing on the cake, on an issue I worked on years before my current job.”

Vitter, who is the ranking Republican of the Senate Environment and Public Works Committee and a frequent EPA critic, specifically highlights the mention of McCarthy, who is about to undergo the Senate confirmation process.

“It appears there’s a collective strategy at the EPA to punish energy producers, but also an effort towards ‘shaming the states,’” Vitter said in the announcement of Tuesday’s letter to McCarthy. “The EPA’s nominee, Gina McCarthy, created a rule that was apparently the ‘icing on the cake’ to this shocking strategy. If she wants to become the administrator, an immediate and fully transparent response to this is absolutely necessary.”

Vitter has called outgoing EPA Administrator Lisa Jackson, of New Orleans, the worst ever in her job.

The EPA did not respond to media requests for comment on Tuesday afternoon.

Republicans on Vitter’s committee have investigated Armendariz, as well as the alleged use of private email addresses by EPA employees to conduct business to avoid government transparency. The EPA has denied that Jackson and others have used private email address in violation of internal employee standards.

The letter sent on Tuesday by Vitter and other Republicans demands answers for a variety of concerns about regulations and email interactions by March 22.

“As the President’s nominee to be Administrator, we require your immediate attention to the questions that have been raised by these documents,” the letter states. “Failure to respond in a prompt and fully transparent fashion will leave a cloud of doubt over whether you intend to break with your predecessor and truly lead a transparent agency.”

As for Armendariz, he lost his job after a video of comments he made in 2010 surfaced last year. In the video, he was discussing strategies to bring oil and gas companies that were skirting rules to comply with federal regulations.

He compared the strategies with ancient Roman armies going to conquer small villages and executing the first five people they saw in order to quell the villages into submission.

“And so you make examples out of people who are, in this case, not compliant with the law,” Armendariz said in the video. “Find people who are not compliant with the law, and you hit them as hard as you can, and you make examples out of them, and there is a deterrent effect there.

“And, companies that are smart see that, they don’t want to play that game and they decide at that point that it’s time to clean up,” he added.