Former Environmental Protection Agency Administrator Lisa Jackson used her personal email address to conduct official business, including with a corporate lobbyist, in a possible violation of federal record-keeping laws.

The new emails came to light as the result of a Freedom of Information Act request from the Competitive Enterprise Institute. Christopher Horner, a fellow at the conservative free-market group, uncovered Jackson’s use of a secondary email account under the alias of “Richard Windsor.”

The name of that email account was made up of the name of Jackson’s dog and her hometown, and it used an domain. But the CEI review of a new trove of emails found that Jackson also used a different private personal email account to conduct official business.

In one email string, Jackson advises Alison Taylor, a vice president at Siemens Corp., to use her “home email” when she needs to contact her directly.

Taylor had emailed Jackson at her “Richard Windsor” account on Dec. 8, 2009, and asked whether she “might be able to spare a few minutes to meet with Siemens’ global sustainability office (who is my boss) Barbara Kux.”

“I know this is a busy time for you, and I have explained this to her. She’s a big fan,” Taylor wrote.

Jackson agreed to the meeting but sent a follow-up email with the line: “P.S. Can you use my home email rather than this one when you need to contact me directly? Tx, Lisa.”

Republicans on Capitol Hill have long accused Jackson, as well as other Cabinet officials, of violating federal transparency laws by using personal email to conduct official business. The latest evidence CEI uncovered, they said, is proof that Jackson was the most egregious violator.

“For months this administration has brushed off transparency concerns, especially when it comes to federal record-keeping laws. Former EPA Administrator Jackson, aka ‘Richard Windsor,’ has been the biggest culprit,” said Sen. David Vitter, the top Republican on the Environment and Public Works Committee.

Since the first evidence of using personal emails or aliases for official business was uncovered, the EPA has promised to review and revamp its email practices and policies.

Vitter and Rep. Darrell Issa, chairman of the House Oversight and Government Reform Committee, have partnered on an investigation of improper record-keeping practices within the Obama administration.

Issa called the latest email evidence “troubling” and said it shows that President Obama’s Cabinet regularly undermined his promise to run the most transparent administration in history and “creates an undeniable impression that officials are engaging in inappropriate behavior.”

In May, Apple hired Jackson to head its environmental efforts. She had worked for the Obama administration for four years, resigning in February.